cgen: fix nested or expr call (fix #18803) (#18807)

vlib/v/gen/c/cgen.v

@@ -6115,11 +6115,8 @@ fn (mut g Gen) or_block(var_name string, or_block ast.OrExpr, return_type ast.Ty
 	}
 	if or_block.kind == .block {
 		g.or_expr_return_type = return_type.clear_flags(.option, .result)
-		if g.inside_or_block {
-			g.writeln('\terr = ${cvar_name}.err;')
-		} else {
 		g.writeln('\tIError err = ${cvar_name}.err;')
-		}
+
 		g.inside_or_block = true
 		defer {
 			g.inside_or_block = false

vlib/v/tests/nested_or_expr_call_test.v

@@ -0,0 +1,18 @@
+fn get_name() !string {
+	return error('failed')
+}
+
+fn test_nested_or_expr_call() {
+	uid_map := map[int]string{}
+	uid := 2
+	username := if uid <= 0 {
+		'unknown'
+	} else {
+		uid_map[uid] or {
+			name := get_name() or { 'unknown' }
+			name
+		}
+	}
+	assert username == 'unknown'
+	println('${uid} is ${username}')
+}