Fix bug in gzclose_w() when gzwrite() fails to allocate memory.

gzwrite.c

@@ -547,6 +547,7 @@ int ZEXPORT gzclose_w(file)
     }
 
     /* flush, free memory, and close file */
+    if (state->size) {
         if (gz_comp(state, Z_FINISH) == -1)
             ret = state->err;
         if (!state->direct) {
@@ -554,6 +555,7 @@ int ZEXPORT gzclose_w(file)
             free(state->out);
         }
         free(state->in);
+    }
     gz_error(state, Z_OK, NULL);
     free(state->path);
     if (close(state->fd) == -1)