node: simplify some substr->slice expressions

node.go

@@ -1254,6 +1254,10 @@ func (this *conversionState) convertNoFreeFloating(n_ node.Node) (string, error)
 			} else if len(callParams) == 3 {
 				// if lnum, ok := n.ArgumentList.Arguments[1].
 
+				if callParams[1] == `0` {
+					return "(" + callParams[0] + ")[:" + callParams[2] + "]", nil
+				}
+
 				// WARNING: We are doubling up on the first parameter
 				// This is a problem if it's not necessarily constant