Fix #79497: Fix php_openssl_subtract_timeval()

I stumbled upon this while debugging a strange issue with
stream_socket_client() where it randomly throws out errors when
the connection timeout is set to below 1s. The logic to calculate
time difference in php_openssl_subtract_timeval() is wrong when
a.tv_usec < b.tv_usec, causing connection errors before the timeout
is reached.

Author: joec4i

NEWS

@@ -15,6 +15,10 @@ PHP                                                                        NEWS
   . Fixed bug #79441 (Segfault in mb_chr() if internal encoding is unsupported).
     (Girgias)
 
+- OpenSSL:
+  . Fixed bug #79497 (stream_socket_client() throws an unknown error sometimes
+    with <1s timeout). (Joe Cai)
+
 - Standard:
   . Fixed bug #79468 (SIGSEGV when closing stream handle with a stream filter
     appended). (dinosaur)

ext/openssl/xp_ssl.c

@@ -2209,8 +2209,8 @@ static struct timeval php_openssl_subtract_timeval(struct timeval a, struct time
 	difference.tv_usec = a.tv_usec - b.tv_usec;
 
 	if (a.tv_usec < b.tv_usec) {
-	  	b.tv_sec  -= 1L;
-	   	b.tv_usec += 1000000L;
+		difference.tv_sec  -= 1L;
+		difference.tv_usec += 1000000L;
 	}
 
 	return difference;