[bugfix][server] Fix prefix path for server

Fixes #18230 - service configuration error (service unknown or unsupported)

I though about placing the fix into the server code, but I believe
that it's much more cleaner here: otherwise we'd need to adjust all
other paths *after* they were uncorrectly set by the application
init() code.

Author: elpaso

src/core/qgsapplication.cpp

@@ -220,7 +220,12 @@ void QgsApplication::init( QString profileFolder )
       setPrefixPath( myPrefix, true );
 #else
       QDir myDir( applicationDirPath() );
-      myDir.cdUp();
+      // Fix for server wich is one level deeper in /usr/lib/cgi-bin
+      if ( applicationDirPath().contains( QStringLiteral( "cgi-bin" ) ) )
+      {
+        myDir.cdUp();
+      }
+      myDir.cdUp(); // Go from /usr/bin or /usr/lib (for server) to /usr
       QString myPrefix = myDir.absolutePath();
       setPrefixPath( myPrefix, true );
 #endif