BUG: #7416 fix error when jpeg is not found

Modules/FindJPEG.cmake

@@ -23,6 +23,8 @@ ENDIF(JPEG_FOUND)
 
 # Deprecated declarations.
 SET (NATIVE_JPEG_INCLUDE_PATH ${JPEG_INCLUDE_DIR} )
-GET_FILENAME_COMPONENT (NATIVE_JPEG_LIB_PATH ${JPEG_LIBRARY} PATH)
+IF(JPEG_LIBRARY)
+  GET_FILENAME_COMPONENT (NATIVE_JPEG_LIB_PATH ${JPEG_LIBRARY} PATH)
+ENDIF(JPEG_LIBRARY)
 
 MARK_AS_ADVANCED(JPEG_LIBRARY JPEG_INCLUDE_DIR )