fix #37395 (recursive mkdir() fails to create nonexistent directories in root dir)

NEWS

@@ -38,7 +38,9 @@ PHP                                                                        NEWS
 - Added pg_field_table() function. (Edin)
 - Added implementation of curl_multi_info_read(). (Brian)
 - Added RFC2397 (data: stream) support. (Marcus)
-- Fixed Bug #37457 (Crash when an exception is thrown in accept() method of 
+- Fixed bug #37395 (recursive mkdir() fails to create nonexistent directories 
+  in root dir). (Tony)
+- Fixed bug #37457 (Crash when an exception is thrown in accept() method of 
   FilterIterator). (Marcus)
 - Fixed bug #37416 (iterator_to_array() hides exceptions thrown in rewind()
   method). (Tony)

main/streams/plain_wrapper.c

@@ -1100,7 +1100,7 @@ static int php_plain_files_mkdir(php_stream_wrapper *wrapper, char *dir, int mod
 		}
 		else {
 			/* find a top level directory we need to create */
-			while ( (p = strrchr(buf + offset, DEFAULT_SLASH)) || (p = strrchr(buf, DEFAULT_SLASH)) ) {
+			while ( (p = strrchr(buf + offset, DEFAULT_SLASH)) || ( offset !=1 && (p = strrchr(buf, DEFAULT_SLASH))) ) {
 				*p = '\0';
 				if (VCWD_STAT(buf, &sb) == 0) {
 					*p = DEFAULT_SLASH;