FindZLIB: only set INCLUDE_DIRECTORIES/LIBRARIES if zlib is found

Modules/FindZLIB.cmake

@@ -41,12 +41,13 @@ IF (ZLIB_INCLUDE_DIR)
     STRING(REGEX REPLACE ".*#define ZLIB_VERSION \"([0-9]+)\\.([0-9]+)\\.([0-9]+)\".*" "\\1.\\2.\\3" ZLIB_VERSION_STRING "${ZLIB_H}")
 ENDIF()
 
-# Per-recommendation
-SET(ZLIB_INCLUDE_DIRS "${ZLIB_INCLUDE_DIR}")
-SET(ZLIB_LIBRARIES    "${ZLIB_LIBRARY}")
-
 # handle the QUIETLY and REQUIRED arguments and set ZLIB_FOUND to TRUE if 
 # all listed variables are TRUE
 INCLUDE(FindPackageHandleStandardArgs)
-FIND_PACKAGE_HANDLE_STANDARD_ARGS(ZLIB DEFAULT_MSG ZLIB_LIBRARIES ZLIB_INCLUDE_DIRS)
+FIND_PACKAGE_HANDLE_STANDARD_ARGS(ZLIB DEFAULT_MSG ZLIB_INCLUDE_DIR ZLIB_LIBRARY)
+
+IF (ZLIB_FOUND)
+    SET(ZLIB_INCLUDE_DIRS ${ZLIB_INCLUDE_DIR})
+    SET(ZLIB_LIBRARIES    ${ZLIB_LIBRARY})
+ENDIF()