tree-wide: check if errno is greater than zero (2)

Compare errno with zero in a way that tells gcc that
(if the condition is true) errno is positive.

src/core/execute.c

@@ -2683,7 +2683,7 @@ void exec_context_dump(ExecContext *c, FILE* f, const char *prefix) {
                 fputc('\n', f);
         }
 
-        if (c->syscall_errno != 0)
+        if (c->syscall_errno > 0)
                 fprintf(f,
                         "%sSystemCallErrorNumber: %s\n",
                         prefix, strna(errno_to_name(c->syscall_errno)));