Update test/fpm_test/test_filesystem.f90

Co-authored-by: Laurence Kedward <laurence.kedward@bristol.ac.uk>

Author: freevryheid

test/fpm_test/test_filesystem.f90

@@ -168,6 +168,7 @@ subroutine check_rmdir(error, path)
         if (.not. is_dir(path)) then
             call test_failed(error, &
                 "Directory path "//path//" doesn't exist before its deletion")
+            return
         end if
 
         ! Delete directory