Removing 'if' branch from the fix.

This new error shouldn't be distinguishable from other padding errors.
Updating 'bad' instead of adding a new 'if' branch.
diff --git a/library/rsa.c b/library/rsa.c
index 2baf532..4c85c29 100644
--- a/library/rsa.c
+++ b/library/rsa.c
@@ -856,8 +856,7 @@
         bad |= *p++; /* Must be zero */
     }
 
-    if( pad_count < 8 )
-        return( MBEDTLS_ERR_RSA_BAD_INPUT_DATA );
+    bad |= ( pad_count < 8 );
 
     if( bad )
         return( MBEDTLS_ERR_RSA_INVALID_PADDING );