fix runtime warning

Author: jef-n

src/core/qgsapplication.cpp

@@ -331,7 +331,10 @@ const QString QgsApplication::prefixPath()
 {
   if ( ABISYM( mRunningFromBuildDir ) )
   {
-    qWarning( "!!! prefix path was requested, but it is not valid - we do not run from installed path !!!" );
+    static bool once = true;
+    if ( once )
+      qWarning( "!!! prefix path was requested, but it is not valid - we do not run from installed path !!!" );
+    once = false;
   }
 
   return ABISYM( mPrefixPath );

src/core/qgsmaplayer.cpp

@@ -922,7 +922,7 @@ bool QgsMapLayer::loadNamedStyleFromDb( const QString &db, const QString &theURI
 
   QgsDebugMsg( QString( "Trying to load style for \"%1\" from \"%2\"" ).arg( theURI ).arg( db ) );
 
-  if ( !QFile( db ).exists() )
+  if ( db.isEmpty() || !QFile( db ).exists() )
     return false;
 
   myResult = sqlite3_open_v2( db.toUtf8().data(), &myDatabase, SQLITE_OPEN_READONLY, NULL );