Town directory window: Only resort on population change if necessary

src/town.h

@@ -204,6 +204,7 @@ enum TownRatingCheckType {
 enum TownDirectoryInvalidateWindowData {
 	TDIWD_FORCE_REBUILD,
 	TDIWD_FILTER_CHANGES,        ///< The filename filter has changed (via the editbox)
+	TDIWD_POPULATION_CHANGE,
 	TDIWD_FORCE_RESORT,
 };
 

src/town_cmd.cpp

@@ -548,7 +548,7 @@ static void ChangePopulation(Town *t, int mod)
 	InvalidateWindowData(WC_TOWN_VIEW, t->index); // Cargo requirements may appear/vanish for small populations
 	if (_settings_client.gui.population_in_label) t->UpdateVirtCoord();
 
-	InvalidateWindowData(WC_TOWN_DIRECTORY, 0, TDIWD_FORCE_RESORT);
+	InvalidateWindowData(WC_TOWN_DIRECTORY, 0, TDIWD_POPULATION_CHANGE);
 }
 
 /**

src/town_gui.cpp

@@ -1001,6 +1001,11 @@ public:
 					this->vscroll->SetCount((int)this->towns.size()); // Update scrollbar as well.
 				}
 				break;
+
+			case TDIWD_POPULATION_CHANGE:
+				if (this->towns.SortType() == 1) this->towns.ForceResort();
+				break;
+
 			default:
 				this->towns.ForceResort();
 		}