FindPhysFS: use find_package_handle_standard_args()

Modules/FindPhysFS.cmake

@@ -54,8 +54,8 @@ FIND_LIBRARY(PHYSFS_LIBRARY
   /opt
 )
 
-SET(PHYSFS_FOUND "NO")
-IF(PHYSFS_LIBRARY AND PHYSFS_INCLUDE_DIR)
-  SET(PHYSFS_FOUND "YES")
-ENDIF(PHYSFS_LIBRARY AND PHYSFS_INCLUDE_DIR)
+# handle the QUIETLY and REQUIRED arguments and set PHYSFS_FOUND to TRUE if
+# all listed variables are TRUE
+INCLUDE(FindPackageHandleStandardArgs)
+FIND_PACKAGE_HANDLE_STANDARD_ARGS(PhysFS DEFAULT_MSG PHYSFS_LIBRARY PHYSFS_INCLUDE_DIR)