tdf#95795 vcl: fix KDE5 desktop detection

Regression from commit 6c80a8fe (new
loplugin: oncevar, 2015-11-06), KDE4 was detected as KDE5.

Change-Id: If4a7a074052a31c7505f53c03a36a0975d71b3a7

vcl/unx/generic/desktopdetect/desktopdetector.cxx

@@ -271,7 +271,7 @@ static bool is_kde5_desktop( Display* pDisplay )
 {
     static const char * pFullVersion = getenv( "KDE_FULL_SESSION" );
     static const char * pSessionVersion = getenv( "KDE_SESSION_VERSION" );
-    if ( pFullVersion && pSessionVersion && strcmp(pSessionVersion, "5") )
+    if ( pFullVersion && pSessionVersion && strcmp(pSessionVersion, "5") == 0)
         return true;
 
     if ( KDEVersion( pDisplay ) == 5 )