Ensure name not null in EVP_get_cipherbyname

This adds a check to EVP_get_cipherbyname which ensures that name
is not null when passed to OPENSSL_strcasecmp, which cannot handle
null values.

OpenSSL already ensures this in their implementation of
EVP_get_cipherbyname by using OBJ_NAME_get, so this improves parity.

Change-Id: Icea45a5da2a7a461d2a65fbfbc84653c4f124dab
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/47844
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>

crypto/cipher_extra/cipher_extra.c

@@ -89,6 +89,10 @@ const EVP_CIPHER *EVP_get_cipherbynid(int nid) {
 }
 
 const EVP_CIPHER *EVP_get_cipherbyname(const char *name) {
+  if (name == NULL) {
+    return NULL;
+  }
+
   if (OPENSSL_strcasecmp(name, "rc4") == 0) {
     return EVP_rc4();
   } else if (OPENSSL_strcasecmp(name, "des-cbc") == 0) {