src: remove superfluous check in backtrace_posix.cc

The error check doesn't matter because a failure would be ignored
as part of the loop condition.

PR-URL: #16950
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>

src/backtrace_posix.cc

@@ -25,9 +25,6 @@ void DumpBacktrace(FILE* fp) {
 #if HAVE_EXECINFO_H
   void* frames[256];
   const int size = backtrace(frames, arraysize(frames));
-  if (size <= 0) {
-    return;
-  }
   for (int i = 1; i < size; i += 1) {
     void* frame = frames[i];
     fprintf(fp, "%2d: ", i);