ci: fix sanitize job failures after 02b889d

vlib/v/gen/c/match.v

@@ -183,6 +183,7 @@ fn (mut g Gen) match_expr_sumtype(node ast.MatchExpr, is_expr bool, cond_var str
 }
 
 fn (mut g Gen) match_expr_switch(node ast.MatchExpr, is_expr bool, cond_var string, tmp_var string, enum_typ ast.TypeSymbol) {
+	cname := '${enum_typ.cname}__'
 	mut covered_enum := []string{cap: (enum_typ.info as ast.Enum).vals.len} // collects missing enum variant branches to avoid cstrict errors
 	mut range_branches := []ast.MatchBranch{cap: node.branches.len} // branches have RangeExpr cannot emit as switch case branch, we handle it in default branch
 	mut default_generated := false
@@ -191,6 +192,11 @@ fn (mut g Gen) match_expr_switch(node ast.MatchExpr, is_expr bool, cond_var stri
 	g.indent++
 	for branch in node.branches {
 		if branch.is_else {
+			for val in (enum_typ.info as ast.Enum).vals {
+				if val !in covered_enum {
+					g.writeln('case $cname$val:')
+				}
+			}
 			g.writeln('default:')
 			default_generated = true
 			if range_branches.len > 0 {

vlib/v/gen/c/testdata/enum_switch_case.c.must_have

@@ -1,4 +1,5 @@
 case main__Enum__e1:
 case main__Enum__e4:
+case main__Enum__e6:
 default:
-(e >= 4 && e <= 5)
+(e >= 4 && e <= 5)