v.markused: process the init statements in for init; cond; inc { too (#22908)

vlib/v/markused/walker.v

@@ -154,8 +154,15 @@ pub fn (mut w Walker) stmt(node_ ast.Stmt) {
 			w.fn_decl(mut node)
 		}
 		ast.ForCStmt {
-			w.expr(node.cond)
-			w.stmt(node.inc)
+			if node.has_init {
+				w.stmt(node.init)
+			}
+			if node.has_cond {
+				w.expr(node.cond)
+			}
+			if node.has_inc {
+				w.stmt(node.inc)
+			}
 			w.stmts(node.stmts)
 		}
 		ast.ForInStmt {
@@ -179,7 +186,9 @@ pub fn (mut w Walker) stmt(node_ ast.Stmt) {
 			}
 		}
 		ast.ForStmt {
-			w.expr(node.cond)
+			if !node.is_inf {
+				w.expr(node.cond)
+			}
 			w.stmts(node.stmts)
 		}
 		ast.Return {

vlib/v/tests/skip_unused/for_c_stmt.run.out

@@ -0,0 +1,5 @@
+ok
+12
+13
+14
+ok

vlib/v/tests/skip_unused/for_c_stmt.skip_unused.run.out

@@ -0,0 +1,5 @@
+ok
+12
+13
+14
+ok

vlib/v/tests/skip_unused/for_c_stmt.vv

@@ -0,0 +1,10 @@
+const abc = 12
+
+fn main() {
+	println('ok')
+	for x := abc; x<15;x++ {
+		println(x)
+	}
+	println('ok')
+}
+