COMP: add quote in case the string is empty

CMakeLists.txt

@@ -83,7 +83,7 @@ IF(Mercurial_FOUND)
   ELSE(OTB_WC_STATUS)
     MESSAGE(STATUS "No files modified locally")
   ENDIF(OTB_WC_STATUS)
-  STRING(REGEX REPLACE "\n" ";" OTB_WC_STATUS ${OTB_WC_STATUS})
+  STRING(REGEX REPLACE "\n" ";" OTB_WC_STATUS "${OTB_WC_STATUS}")
   SET(OTB_WC_STATUS ${OTB_WC_STATUS} CACHE STRING "Repository status" FORCE)
 ENDIF(Mercurial_FOUND)