BUG: Watch for empty qconfig.pri files. Fixes #7287.

Modules/FindQt4.cmake

@@ -1343,9 +1343,9 @@ IF (QT4_QMAKE_FOUND)
   #######################################
   IF(EXISTS "${QT_MKSPECS_DIR}/qconfig.pri")
     FILE(READ ${QT_MKSPECS_DIR}/qconfig.pri _qconfig_FILE_contents)
-    STRING(REGEX MATCH "QT_CONFIG[^\n]+" QT_QCONFIG ${_qconfig_FILE_contents})
-    STRING(REGEX MATCH "CONFIG[^\n]+" QT_CONFIG ${_qconfig_FILE_contents})
-    STRING(REGEX MATCH "EDITION[^\n]+" QT_EDITION ${_qconfig_FILE_contents})
+    STRING(REGEX MATCH "QT_CONFIG[^\n]+" QT_QCONFIG "${_qconfig_FILE_contents}")
+    STRING(REGEX MATCH "CONFIG[^\n]+" QT_CONFIG "${_qconfig_FILE_contents}")
+    STRING(REGEX MATCH "EDITION[^\n]+" QT_EDITION "${_qconfig_FILE_contents}")
   ENDIF(EXISTS "${QT_MKSPECS_DIR}/qconfig.pri")
   IF("${QT_EDITION}" MATCHES "DesktopLight")
     SET(QT_EDITION_DESKTOPLIGHT 1)