Fix #80648: Fix for bug 79296 should be based on runtime version

Instead of checking for actually affected libzip versions, we now always
`ZIP_TRUNCATE` empty files unless `ZIP_RDONLY` is set.

Closes GH-6625.

Author: cmb69

NEWS

@@ -2,6 +2,10 @@ PHP                                                                        NEWS
 |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 ?? ??? 2021, PHP 7.4.16
 
+- Zip:
+  . Fixed bug #80648 (Fix for bug 79296 should be based on runtime version).
+    (cmb, Remi)
+
 21 Jan 2021, PHP 7.4.15
 
 - Core:

ext/zip/php_zip.c

@@ -1473,20 +1473,21 @@ static ZIPARCHIVE_METHOD(open)
 		ze_obj->filename = NULL;
 	}
 
-#if LIBZIP_VERSION_MAJOR > 1 || LIBZIP_VERSION_MAJOR == 1 && LIBZIP_VERSION_MINOR >= 6
-	/* reduce BC break introduce in libzip 1.6.0
-	   "Do not accept empty files as valid zip archives any longer" */
-
 	/* open for write without option to empty the archive */
+#ifdef ZIP_RDONLY
 	if ((flags & (ZIP_TRUNCATE | ZIP_RDONLY)) == 0) {
+#else
+	if ((flags & ZIP_TRUNCATE) == 0) {
+#endif
 		zend_stat_t st;
 
 		/* exists and is empty */
 		if (VCWD_STAT(resolved_path, &st) == 0 && st.st_size == 0) {
+			/* reduce BC break introduced in libzip 1.6.0
+			   "Do not accept empty files as valid zip archives any longer" */
 			flags |= ZIP_TRUNCATE;
 		}
 	}
-#endif
 
 	intern = zip_open(resolved_path, flags, &err);
 	if (!intern || err) {