parser: fix last_line of no body C struct (#9809)

vlib/v/fmt/tests/structs_expected.vv

@@ -58,3 +58,5 @@ pub:
 14
 	*/
 }
+
+struct C.Foo {}

vlib/v/fmt/tests/structs_input.vv

@@ -61,3 +61,5 @@ somefield4 int
 14
 */
 }
+
+struct C.Foo

vlib/v/parser/struct.v

@@ -96,7 +96,7 @@ fn (mut p Parser) struct_decl() ast.StructDecl {
 	mut is_field_mut := false
 	mut is_field_pub := false
 	mut is_field_global := false
-	mut last_line := -1
+	mut last_line := p.prev_tok.position().line_nr + 1
 	mut end_comments := []ast.Comment{}
 	if !no_body {
 		p.check(.lcbr)