cgen: remove the extra generated parentheses of single in_expr (fix #12158) (#12168)

vlib/v/gen/c/cgen.v

@@ -5051,12 +5051,27 @@ fn (mut g Gen) if_expr(node ast.IfExpr) {
 					}
 				}
 				else {
+					mut no_needs_par := false
+					if branch.cond is ast.InfixExpr {
+						if branch.cond.op == .key_in && branch.cond.left !is ast.InfixExpr
+							&& branch.cond.right is ast.ArrayInit {
+							no_needs_par = true
+						}
+					}
+					if no_needs_par {
+						g.write('if ')
+					} else {
 						g.write('if (')
+					}
 					g.expr(branch.cond)
+					if no_needs_par {
+						g.writeln(' {')
+					} else {
 						g.writeln(') {')
 					}
 				}
 			}
+		}
 		if needs_tmp_var {
 			g.stmts_with_tmp_var(branch.stmts, tmp)
 		} else {