Bug 1711836 - Fix GCC warning about the use of strncpy in SandboxBroker::ThreadMain. r=jld

Differential Revision: https://phabricator.services.mozilla.com/D115449

security/sandbox/linux/broker/SandboxBroker.cpp

@@ -738,7 +738,7 @@ void SandboxBroker::ThreadMain(void) {
       // 0 immediately (we nulled the buffer before receiving).
       // We do not assume the second path is 0-terminated, this is
       // enforced below.
-      strncpy(pathBuf2, recvBuf + first_len + 1, kMaxPathLen + 1);
+      strncpy(pathBuf2, recvBuf + first_len + 1, kMaxPathLen);
 
       // First string is guaranteed to be 0-terminated.
       pathLen = first_len;