Add OverflowError and use it for small int overflow instead of assert.
diff --git a/py/mpqstrraw.h b/py/mpqstrraw.h
index 6674a2c..328cb73 100644
--- a/py/mpqstrraw.h
+++ b/py/mpqstrraw.h
@@ -32,6 +32,7 @@
 Q(SyntaxError)
 Q(TypeError)
 Q(ValueError)
+Q(OverflowError)
 
 Q(abs)
 Q(all)