MenuButton: Don't crash anymore when triggering the MenuButton shortcut.

[GB.FORM]
* BUG: MenuButton: Don't crash anymore when triggering the MenuButton shortcut.
* NEW: Add icon for Gambas 3 application in Gambas icon set.

comp/src/gb.form/.project

 # Gambas Project File 3.0
 Title=More controls for graphical components
-Startup=FTestFileView
+Startup=FTestDateChooser
 Icon=.hidden/icon.png
 Version=3.17.90
 VersionFile=1

comp/src/gb.form/.src/Button/MenuButton.class

@@ -235,7 +235,7 @@ Private Sub Arrow_Click()
     Return
   Endif
   
-  DrawingArea_MouseUp
+  Try DrawingArea_MouseUp
   HandleMenu(Me)
   
 End

comp/src/gb.form/map/icon.map

@@ -160,7 +160,7 @@ font                    [-breeze*]actions/format-text-superscript;preferences/pr
 formula                 actions/formula
 forward                 actions/media-seek-forward
 fullscreen              actions/view-fullscreen
-gambas                  #
+gambas                  #;;apps/gambas3
 game                    categories/applications-games;devices/input-gaming;devices/joystick;;preferences/preferences-desktop-gaming;apps/preferences-desktop-gaming
 gamma                   #
 gnu                     #