Spot when we didn't successfully create an RSA public key from a

public blob, and return a proper error in that situation rather than a
struct with unhelpful NULLs in.

[originally from svn r9991]

sshrsa.c

@@ -561,6 +561,8 @@ static Bignum getmp(char **data, int *datalen)
     return b;
 }
 
+static void rsa2_freekey(void *key);   /* forward reference */
+
 static void *rsa2_newkey(char *data, int len)
 {
     char *p;
@@ -580,6 +582,11 @@ static void *rsa2_newkey(char *data, int len)
     rsa->p = rsa->q = rsa->iqmp = NULL;
     rsa->comment = NULL;
 
+    if (!rsa->exponent || !rsa->modulus) {
+        rsa2_freekey(rsa);
+        return NULL;
+    }
+
     return rsa;
 }