DoIgnore Missing Payload Bounds Validation

The DoIgnore() function was not bounds checking the ignore message.
Changed it to use the GetSkip() function which does bounds checking and
skips the current blob. Updated GetSkip() to allow 0 length blobs to
skip.

Affected function: DoIgnore.
Issue: F-410

Author: ejohnstown

src/internal.c

@@ -3575,12 +3575,12 @@ int GetSkip(const byte* buf, word32 len, word32* idx)
     int result;
     word32 sz;
 
-    result = GetUint32(&sz, buf, len, idx);
+    result = GetSize(&sz, buf, len, idx);
 
     if (result == WS_SUCCESS) {
         result = WS_BUFFER_E;
 
-        if (*idx < len && sz <= len - *idx) {
+        if (*idx <= len && sz <= len - *idx) {
             *idx += sz;
             result = WS_SUCCESS;
         }
@@ -6320,18 +6320,8 @@ static int DoKexDhGexGroup(WOLFSSH* ssh,
 
 static int DoIgnore(WOLFSSH* ssh, byte* buf, word32 len, word32* idx)
 {
-    word32 dataSz;
-    word32 begin = *idx;
-
     WOLFSSH_UNUSED(ssh);
-    WOLFSSH_UNUSED(len);
-
-    ato32(buf + begin, &dataSz);
-    begin += LENGTH_SZ + dataSz;
-
-    *idx = begin;
-
-    return WS_SUCCESS;
+    return GetSkip(buf, len, idx);
 }
 
 static int DoRequestSuccess(WOLFSSH *ssh, byte *buf, word32 len, word32 *idx)