[#158] client: Do not ignore errors in `processCall()`

Some callbacks, such as `close()` -> `result(v2)` may
generate new errors, so `processCall` should not ignore
them.

Signed-off-by: Alex Vanin <alexey@nspcc.ru>

client/common.go

@@ -255,8 +255,11 @@ func (x *contextCall) processCall() bool {
 
 	// close and write response to resulting structure
 	ok = x.close()
+	if !ok {
+		return false
+	}
 
-	return ok
+	return x.err == nil
 }
 
 // initializes static cross-call parameters inherited from client.