Simplify filament_presence_check usage

Pull all checks needed into the function such that the caller
only needs to check the return value

Also added description for the filament_presence_check function

Firmware/Marlin_main.cpp

@@ -5224,17 +5224,10 @@ void process_commands()
       lcd_resume_print();
     else
     {
-        if (!MMU2::mmu2.Enabled()) {
-            // Check if the filament is present before starting a print.
-            // When MMU is enabled, this is not necessary and the G-code file
-            // should always tell the MMU which filament to load.
-            filament_presence_check();
-
-            if (lcd_commands_type == LcdCommands::StopPrint) {
-                // Print job was canceled
-                break;
-            }
-        }
+      if (!filament_presence_check()) {
+        // Print was aborted
+        break;
+      }
 
       if (!card.get_sdpos())
       {
@@ -5866,16 +5859,9 @@ Sigma_Exit:
     */
     case 75:
     {
-        if (!MMU2::mmu2.Enabled()) {
-            // Check if the filament is present before starting a host print.
-            // When MMU is enabled, this is not necessary and the G-code file
-            // should always tell the MMU which filament to load.
-            filament_presence_check();
-
-            if (lcd_commands_type == LcdCommands::StopPrint) {
-                // Print job was canceled
-                break;
-            }
+        if (!filament_presence_check()) {
+          // Print was aborted
+          break;
         }
 
         print_job_timer.start();

Firmware/util.cpp

@@ -371,19 +371,32 @@ void fw_version_check(const char *pVersion) {
     );
 }
 
-void filament_presence_check() {
-    if (fsensor.isEnabled() && !fsensor.getFilamentPresent())
-    {
-        if (oCheckFilament == ClCheckMode::_None)
-            return;
+bool filament_presence_check() {
+    // When MMU is enabled, this is not necessary and the G-code file
+    // should always tell the MMU which filament to load.
+    if (MMU2::mmu2.Enabled()) {
+        goto done;
+    }
+
+    if (fsensor.isEnabled() && !fsensor.getFilamentPresent()) {
+        if (oCheckFilament == ClCheckMode::_None) {
+            goto done;
+        }
 
         render_M862_warnings(
             _T(MSG_MISSING_FILAMENT_CONTINUE)
             ,_T(MSG_MISSING_FILAMENT_CANCELLED)
             ,(uint8_t)oCheckFilament
         );
+
+        if (lcd_commands_type == LcdCommands::StopPrint) {
+            // Print job was canceled
+            return false;
+        }
     }
-    
+
+done:
+    return true;
 }
 
 void gcode_level_check(uint16_t nGcodeLevel) {

Firmware/util.h

@@ -115,9 +115,22 @@ void nozzle_diameter_check(uint16_t nDiameter);
 void printer_model_check(uint16_t nPrinterModel, uint16_t actualPrinterModel);
 void printer_smodel_check(const char *pStrPos, const char *actualPrinterSModel);
 void fw_version_check(const char *pVersion);
-void filament_presence_check();
 void gcode_level_check(uint16_t nGcodeLevel);
 
+/// Check if the filament is present before starting a print job.
+/// Depending on the check level set in the menus the printer will:
+///   - None: not issue any warning about missing filament
+///   - Warning (default): The user is warned about missing filament
+///     and is prompted to continue with Yes/No. If No is selected,
+///     the print is aborted. If no user input is given (e.g. from
+///     host printing) then the warning will expire in 30 seconds and
+///     the printer assumes the Yes option was selected.
+///   - Strict: If the filament is not detected when a print is started,
+///     it is immediately canceled with a message saying the filament is
+///     missing.
+/// @returns false if the print is canceled, true otherwise
+bool filament_presence_check();
+
 uint16_t nPrinterType(bool bMMu);
 const char *sPrinterType(bool bMMu);