Validate IV length in the non-streaming path in wc_PKCS7_DecodeEnvelopedData.

Reported by: Jorge Milla (Pig-Tail) <jorge@jmilla.es>

Author: kareem-wolfssl

wolfcrypt/src/pkcs7.c

@@ -13611,6 +13611,12 @@ int wc_PKCS7_DecodeEnvelopedData(wc_PKCS7* pkcs7, byte* in,
                 break;
             }
         #else
+            /* ensure IV bytes are within the input buffer before copying */
+            if (length < 0 || (word32)length > pkiMsgSz ||
+                    idx > pkiMsgSz - (word32)length) {
+                ret = BUFFER_E;
+                break;
+            }
             ret = 0;
         #endif