Bed temperature management refinement

This actually fixes a case where the temperature was not set properly
with one-at-a-time mode

CURA-8889

src/gcodeExport.cpp

@@ -111,19 +111,22 @@ void GCodeExport::preSetup(const size_t start_extruder)
 
     estimateCalculator.setFirmwareDefaults(mesh_group->settings);
 
-    if (mesh_group != scene.mesh_groups.begin())
+    if (mesh_group == scene.mesh_groups.begin())
     {
-        // Current bed temperature is the one of the previous group
-        bed_temperature = (scene.current_mesh_group - 1)->settings.get<Temperature>("material_bed_temperature");
-    }
-    else if (! scene.current_mesh_group->settings.get<bool>("material_bed_temp_prepend"))
-    {
-        // Current bed temperature is the one of the first layer (has already been set in header)
-        bed_temperature = scene.current_mesh_group->settings.get<Temperature>("material_bed_temperature_layer_0");
+        if (! scene.current_mesh_group->settings.get<bool>("material_bed_temp_prepend"))
+        {
+            // Current bed temperature is the one of the first layer (has already been set in header)
+            bed_temperature = scene.current_mesh_group->settings.get<Temperature>("material_bed_temperature_layer_0");
+        }
+        else
+        {
+            // Bed temperature has not been set yet
+        }
     }
     else
     {
-        // Current bed temperature has not been set yet
+        // Current bed temperature is the one of the previous group
+        bed_temperature = (scene.current_mesh_group - 1)->settings.get<Temperature>("material_bed_temperature");
     }
 }
 
@@ -1517,31 +1520,28 @@ void GCodeExport::writeBedTemperatureCommand(const Temperature& temperature, con
     { // The UM2 family doesn't support temperature commands (they are fixed in the firmware)
         return;
     }
-    bool wrote_command = false;
-    if (wait)
+
+    if (bed_temperature != temperature) // Not already at the desired temperature.
     {
-        if (bed_temperature != temperature) // Not already at the desired temperature.
+        if (wait)
         {
             if (flavor == EGCodeFlavor::MARLIN)
             {
                 *output_stream << "M140 S"; // set the temperature, it will be used as target temperature from M105
                 *output_stream << PrecisionedDouble{ 1, temperature } << new_line;
                 *output_stream << "M105" << new_line;
             }
+            *output_stream << "M190 S";
         }
-        *output_stream << "M190 S";
-        wrote_command = true;
-    }
-    else if (bed_temperature != temperature)
-    {
-        *output_stream << "M140 S";
-        wrote_command = true;
-    }
-    if (wrote_command)
-    {
+        else
+        {
+            *output_stream << "M140 S";
+        }
+
         *output_stream << PrecisionedDouble{ 1, temperature } << new_line;
+
+        bed_temperature = temperature;
     }
-    bed_temperature = temperature;
 }
 
 void GCodeExport::writeBuildVolumeTemperatureCommand(const Temperature& temperature, const bool wait)