Fix broken cases of `Seek` usage in `_file_stream_proc`

Handles `EINVAL`, among other fixes.

core/os/file_windows.odin

@@ -192,6 +192,8 @@ seek :: proc(fd: Handle, offset: i64, whence: int) -> (i64, Error) {
 	case 0: w = win32.FILE_BEGIN
 	case 1: w = win32.FILE_CURRENT
 	case 2: w = win32.FILE_END
+	case:
+		return 0, .Invalid_Whence
 	}
 	hi := i32(offset>>32)
 	lo := i32(offset)

core/os/os_windows.odin

@@ -43,6 +43,7 @@ ERROR_BUFFER_OVERFLOW     :: _Platform_Error(111)
 ERROR_INSUFFICIENT_BUFFER :: _Platform_Error(122)
 ERROR_MOD_NOT_FOUND       :: _Platform_Error(126)
 ERROR_PROC_NOT_FOUND      :: _Platform_Error(127)
+ERROR_NEGATIVE_SEEK       :: _Platform_Error(131)
 ERROR_DIR_NOT_EMPTY       :: _Platform_Error(145)
 ERROR_ALREADY_EXISTS      :: _Platform_Error(183)
 ERROR_ENVVAR_NOT_FOUND    :: _Platform_Error(203)
@@ -91,6 +92,9 @@ get_last_error :: proc "contextless" () -> Error {
 	case win32.ERROR_INVALID_HANDLE:
 		return .Invalid_File
 
+	case win32.ERROR_NEGATIVE_SEEK:
+		return .Invalid_Offset
+
 	case
 		win32.ERROR_BAD_ARGUMENTS,
 		win32.ERROR_INVALID_PARAMETER,

core/os/stream.odin

@@ -47,6 +47,14 @@ _file_stream_proc :: proc(stream_data: rawptr, mode: io.Stream_Mode, p: []byte,
 		}
 	case .Seek:
 		n, os_err = seek(fd, offset, int(whence))
+		if os_err != nil {
+			switch whence {
+			case .Start, .Current, .End:
+				return 0, .Invalid_Offset
+			case:
+				return 0, .Invalid_Whence
+			}
+		}
 	case .Size:
 		n, os_err = file_size(fd)
 	case .Destroy:

core/sys/windows/winerror.odin

@@ -213,6 +213,7 @@ ERROR_BROKEN_PIPE            : DWORD : 109
 ERROR_CALL_NOT_IMPLEMENTED   : DWORD : 120
 ERROR_INSUFFICIENT_BUFFER    : DWORD : 122
 ERROR_INVALID_NAME           : DWORD : 123
+ERROR_NEGATIVE_SEEK          : DWORD : 131
 ERROR_BAD_ARGUMENTS          : DWORD : 160
 ERROR_LOCK_FAILED            : DWORD : 167
 ERROR_ALREADY_EXISTS         : DWORD : 183