Fix Windows zlib include path escaping

Author: AnastaZIuk

scripts/cmake/genout.cmake.in

@@ -26,7 +26,7 @@ set(PNG_PREFIX "@PNG_PREFIX@")
 set(PNGLIB_MAJOR "@PNGLIB_MAJOR@")
 set(PNGLIB_MINOR "@PNGLIB_MINOR@")
 set(PNGLIB_VERSION "@PNGLIB_VERSION@")
-set(ZLIBINCDIR "@ZLIB_INCLUDE_DIRS@")
+set(ZLIBINCDIR [===[@ZLIB_INCLUDE_DIRS@]===])
 
 set(PLATFORM_C_FLAGS)
 if(APPLE)