Eliminate creating of unused QString objects in transformCoords

Every call of transformCoords() Qstring dir object is created. It uses
only for output information about errors, so move its creation to error
handling block.

Perfomance gain is ~7%.

Signed-off-by: Yauhen Kharuzhy <jekhor@gmail.com>

Author: jekhor

src/core/qgscoordinatetransform.cpp

@@ -632,14 +632,12 @@ void QgsCoordinateTransform::transformCoords( const int& numPoints, double *x, d
   if ( direction == ReverseTransform )
   {
     projResult = pj_transform( mDestinationProjection, mSourceProjection, numPoints, 0, x, y, z );
-    dir = tr( "inverse transform" );
   }
   else
   {
     Q_ASSERT( mSourceProjection != 0 );
     Q_ASSERT( mDestinationProjection != 0 );
     projResult = pj_transform( mSourceProjection, mDestinationProjection, numPoints, 0, x, y, z );
-    dir = tr( "forward transform" );
   }
 
   if ( projResult != 0 )
@@ -659,6 +657,8 @@ void QgsCoordinateTransform::transformCoords( const int& numPoints, double *x, d
       }
     }
 
+    dir = (direction == ForwardTransform) ? tr( "forward transform" ) : tr( "inverse transform" );
+
     QString msg = tr( "%1 of\n"
                       "%2"
                       "PROJ.4: %3 +to %4\n"