Improve behaviour on fatal errors

If we didn't walk the whole chain, then there may be any kind of errors in the
part of the chain we didn't check, so setting all flags looks like the safe
thing to do.
diff --git a/library/x509_crt.c b/library/x509_crt.c
index d86857d..ee5f27e 100644
--- a/library/x509_crt.c
+++ b/library/x509_crt.c
@@ -2202,11 +2202,14 @@
     mbedtls_x509_sequence *cur = NULL;
     mbedtls_pk_type_t pk_type;
 
-    if( profile == NULL )
-        return( MBEDTLS_ERR_X509_BAD_INPUT_DATA );
-
     *flags = 0;
 
+    if( profile == NULL )
+    {
+        ret = MBEDTLS_ERR_X509_BAD_INPUT_DATA;
+        goto exit;
+    }
+
     if( cn != NULL )
     {
         name = &crt->subject;
@@ -2280,7 +2283,7 @@
         ret = x509_crt_verify_top( crt, parent, ca_crl, profile,
                                    pathlen, selfsigned, flags, f_vrfy, p_vrfy );
         if( ret != 0 )
-            return( ret );
+            goto exit;
     }
     else
     {
@@ -2295,17 +2298,24 @@
             ret = x509_crt_verify_child( crt, parent, trust_ca, ca_crl, profile,
                                          pathlen, selfsigned, flags, f_vrfy, p_vrfy );
             if( ret != 0 )
-                return( ret );
+                goto exit;
         }
         else
         {
             ret = x509_crt_verify_top( crt, trust_ca, ca_crl, profile,
                                        pathlen, selfsigned, flags, f_vrfy, p_vrfy );
             if( ret != 0 )
-                return( ret );
+                goto exit;
         }
     }
 
+exit:
+    if( ret != 0 )
+    {
+        *flags = (uint32_t) -1;
+        return( ret );
+    }
+
     if( *flags != 0 )
         return( MBEDTLS_ERR_X509_CERT_VERIFY_FAILED );