time: fix error for time.local() on windows (#13892)

.github/workflows/ci.yml

@@ -446,6 +446,22 @@ jobs:
         run: .\v.exe test-self
         #    - name: Test
         #      run: .\v.exe test-all
+      - name: Test time functions in a timezone UTC-12
+        run: |
+          tzutil /s "Dateline Standard Time"
+          ./v test vlib/time/
+      - name: Test time functions in a timezone UTC-3
+        run: |
+          tzutil /s "Greenland Standard Time"
+          ./v test vlib/time/
+      - name: Test time functions in a timezone UTC+3
+        run: |
+          tzutil /s "Russian Standard Time"
+          ./v test vlib/time/
+      - name: Test time functions in a timezone UTC+12
+        run: |
+          tzutil /s "New Zealand Standard Time"
+          ./v test vlib/time/
       - name: Test v->js
         run: ./v -o hi.js examples/hello_v_js.v && node hi.js
       - name: Test v binaries

vlib/time/time_windows.c.v

@@ -97,6 +97,9 @@ fn local_as_unix_time() i64 {
 
 // local - return the time `t`, converted to the currently active local timezone
 pub fn (t Time) local() Time {
+	if t.is_local {
+		return t
+	}
 	st_utc := SystemTime{
 		year: u16(t.year)
 		month: u16(t.month)
@@ -140,6 +143,7 @@ fn win_now() Time {
 		second: st_local.second
 		microsecond: st_local.millisecond * 1000
 		unix: st_local.unix_time()
+		is_local: true
 	}
 	return t
 }
@@ -161,6 +165,7 @@ fn win_utc() Time {
 		second: st_utc.second
 		microsecond: st_utc.millisecond * 1000
 		unix: st_utc.unix_time()
+		is_local: false
 	}
 	return t
 }