Avoid dangling pointer in curl header.str

If buf_len is zero, this would leave behind a dangling pointer
to an already released header.str. Make sure this can't happen
by always overwriting the pointer.

Closes GH-7376.

Author: AlexeyZamorov

ext/curl/interface.c

@@ -1766,9 +1766,7 @@ static int curl_debug(CURL *cp, curl_infotype type, char *buf, size_t buf_len, v
 		if (ch->header.str) {
 			zend_string_release_ex(ch->header.str, 0);
 		}
-		if (buf_len > 0) {
-			ch->header.str = zend_string_init(buf, buf_len, 0);
-		}
+		ch->header.str = zend_string_init(buf, buf_len, 0);
 	}
 
 	return 0;