Fix an issue related to the icon property (forms).

An invalid icon file was allowed but the property couldn't be cleared. That's fixed now.

InForm/UiEditor.bas

@@ -522,6 +522,9 @@ SUB __UI_BeforeUpdateDisplay
             IF __UI_ActiveMenu > 0 THEN __UI_DestroyControl Control(__UI_ActiveMenu)
             __UI_Focus = 0
             __UI_ForceRedraw = True
+        ELSEIF CVI(b$) = -6 THEN
+            'User attempted to load an invalid icon file
+            Answer = MessageBox("Only .ico files are accepted.", "", MsgBox_OkOnly + MsgBox_Exclamation)
         END IF
         b$ = MKI$(0): PUT #UiEditorFile, OffsetNewDataFromPreview, b$
 

InForm/UiEditorPreview.bas

@@ -382,8 +382,15 @@ SUB __UI_BeforeUpdateDisplay
                         ELSE
                             _ICON
                             IF _FILEEXISTS(b$) THEN
-                                SendSignal -4
-                                Text(__UI_FormID) = b$
+                                IF LCASE$(RIGHT$(b$, 4)) <> ".ico" THEN
+                                    SendSignal -6
+                                    Text(__UI_FormID) = ""
+                                ELSE
+                                    SendSignal -4
+                                    Text(__UI_FormID) = b$
+                                END IF
+                            ELSE
+                                Text(__UI_FormID) = ""
                             END IF
                         END IF
                     END IF