Add extra (size_t) cast to avoid compiler warning.

Bug: 64575136
Test: builds
Change-Id: Ia33235230b73cb1a828a65dc3a8d1d396fc37d26
(cherry picked from commit 3b126928a1931ed627d736a8023aed2618b57171)
diff --git a/src/rfc1035.c b/src/rfc1035.c
index 265e4df..e440e8a 100755
--- a/src/rfc1035.c
+++ b/src/rfc1035.c
@@ -1144,7 +1144,7 @@
   struct mx_srv_record *rec;
   // Make sure we do not underflow here too.
-  if (qlen > (limit - ((char *)header))) return 0;
+  if (qlen > (size_t)(limit - ((char *)header))) return 0;
   /* If there is an RFC2671 pseudoheader then it will be overwritten by
      partial replies, so we have to do a dry run to see if we can answer