parser: fix error when accessing module without name after dot (#7530)

vlib/v/parser/parser.v

@@ -1147,7 +1147,7 @@ pub fn (mut p Parser) name_expr() ast.Expr {
 				// mark the imported module as used
 				p.register_used_import(p.tok.lit)
 				if p.peek_tok.kind == .dot &&
-					p.peek_tok2.kind != .eof && p.peek_tok2.lit[0].is_capital() {
+					p.peek_tok2.kind != .eof && p.peek_tok2.lit.len > 0 && p.peek_tok2.lit[0].is_capital() {
 					is_mod_cast = true
 				}
 			}

vlib/v/parser/tests/uncomplete_module_call_err.out

@@ -0,0 +1,5 @@
+vlib/v/parser/tests/uncomplete_module_call_err.vv:7:1: error: unexpected token ``
+    5 | fn main() {
+    6 |     os.
+    7 | }
+      | ^

vlib/v/parser/tests/uncomplete_module_call_err.vv

@@ -0,0 +1,7 @@
+module main
+
+import os
+
+fn main() {
+	os.
+}