Linux: Fix incomplete selection check if X11 support is disabled

Author: hluk

src/platform/x11/x11platformclipboard.cpp

@@ -52,7 +52,7 @@ bool isSelectionIncomplete()
 
     return event.state & (Button1Mask | ShiftMask);
 #else
-    return true;
+    return false;
 #endif
 }