internal: add NULL check for ssl arguments

Author: rizlik

src/internal.c

@@ -41806,6 +41806,9 @@ int wolfSSL_GetRecordSize(WOLFSSL *ssl, int payloadSz)
 {
     int recordSize;
 
+    if (ssl == NULL)
+        return BAD_FUNC_ARG;
+
     if (IsEncryptionOn(ssl, 1)) {
         recordSize = BuildMessage(ssl, NULL, 0, NULL, payloadSz, application_data,
              0, 1, 0, CUR_ORDER);
@@ -41837,6 +41840,9 @@ int wolfSSL_GetMaxPlaintextSize(WOLFSSL *ssl)
 {
     int maxFrag;
 
+    if (ssl == NULL)
+        return BAD_FUNC_ARG;
+
     maxFrag = wolfSSL_GetMaxFragSize(ssl);
 
 #if defined(WOLFSSL_DTLS)
@@ -41873,9 +41879,11 @@ int wolfSSL_GetMaxPlaintextSize(WOLFSSL *ssl)
  */
 int wolfSSL_GetMaxFragSize(WOLFSSL* ssl)
 {
-    (void) ssl; /* Avoid compiler warnings */
     int maxFragment;
 
+    if (ssl == NULL)
+        return BAD_FUNC_ARG;
+
     maxFragment = MAX_RECORD_SIZE;
 
 #ifdef HAVE_MAX_FRAGMENT