BUG: Don't clear output strings before using.

Modules/FindQt4.cmake

@@ -1412,8 +1412,8 @@ IF (QT4_QMAKE_FOUND)
       STRING(REPLACE "-L" "" _dbus_query_output "${_dbus_query_output}")
       SEPARATE_ARGUMENTS(_dbus_query_output)
     ELSE(_dbus_result MATCHES 0)
-      SET(_dbus_query_output)
       MESSAGE(WARNING " When querying pkg-config for dbus-1.  An error was reported:\n${_dbus_query_output}")
+      SET(_dbus_query_output)
     ENDIF(_dbus_result MATCHES 0)
 
     FIND_LIBRARY(QT_DBUS_LIBRARY NAMES dbus-1 PATHS ${_dbus_query_output} )
@@ -1440,8 +1440,8 @@ IF (QT4_QMAKE_FOUND)
       STRING(REPLACE "-L" "" _glib_query_output "${_glib_query_output}")
       SEPARATE_ARGUMENTS(_glib_query_output)
     ELSE(_glib_result MATCHES 0)
-      SET(_glib_query_output)
       MESSAGE(WARNING " When querying pkg-config for glib-2.0.  An error was reported:\n${_glib_query_output}")
+      SET(_glib_query_output)
     ENDIF(_glib_result MATCHES 0)
 
     FIND_LIBRARY(QT_GLIB_LIBRARY NAMES glib-2.0 PATHS ${_glib_query_output} )