vfmt: fix eating of `n` in `string(x,n)`

vlib/v/fmt/fmt.v

@@ -788,6 +788,10 @@ pub fn (mut f Fmt) expr(node ast.Expr) {
 			node.typname = f.table.get_type_symbol(node.typ).name
 			f.write(f.type_to_str(node.typ) + '(')
 			f.expr(node.expr)
+			if node.has_arg {
+				f.write(', ')
+				f.expr(node.arg)
+			}
 			f.write(')')
 		}
 		ast.CallExpr {

vlib/v/fmt/tests/to_string_2_forms_keep.vv

@@ -0,0 +1,33 @@
+fn abc() string {
+	unsafe {
+		mut fullpath := vcalloc(4)
+		fullpath[0] = `a`
+		fullpath[1] = `b`
+		fullpath[2] = `c`
+		fullpath[3] = 0
+		return string(fullpath)
+	}
+	return ''
+}
+
+fn def() string {
+	unsafe {
+		mut fullpath := vcalloc(4)
+		fullpath[0] = `a`
+		fullpath[1] = `b`
+		fullpath[2] = `c`
+		fullpath[3] = 0
+		return string(fullpath, 3)
+	}
+	return ''
+}
+
+fn main() {
+	assert 'abc' == abc()
+	assert 'abc' == def()
+	abc_str1 := ptr_str(abc().str)
+	abc_str2 := ptr_str(abc().str)
+	println('abc_str1: $abc_str1')
+	println('abc_str2: $abc_str2')
+	assert abc_str1 != abc_str2
+}