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 43dd2c0..33e673a 100644
--- a/library/rsa.c
+++ b/library/rsa.c
@@ -855,8 +855,7 @@
         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 );