Fix glitch with Selection Tool + Alt (fix aseprite#3976)

Prior to this fix, when the mouse exited and re-entered the editor
area, the Subtract Selection quick command would inadvertently
change to 'rotate shape'.

src/app/ui/editor/editor.cpp

@@ -1915,12 +1915,23 @@ bool Editor::onProcessMessage(Message* msg)
       break;
     }
 
-    case kMouseEnterMessage:
+    case kMouseEnterMessage: {
       m_brushPreview.hide();
-      updateToolLoopModifiersIndicators();
-      updateQuicktool();
-      break;
 
+      // Not update tool loop modifiers when the mouse exits and
+      // re-enters the editor area while the mouse has an
+      // active 'click'.
+      // If it isn't done, when the mouse exits and re-enters the
+      // editor area, the Subtract Selection quick command
+      // (for example) will change to 'rotate shape'.
+      // More details:
+      // https://github.com/aseprite/aseprite/issues/3976
+      if (!hasCapture()) {
+        updateToolLoopModifiersIndicators();
+        updateQuicktool();
+      }
+      break;
+    }
     case kMouseLeaveMessage:
       m_brushPreview.hide();
       StatusBar::instance()->showDefaultText();