fix(gotrue): allow refreshSession with refreshToken when no current session exists

[grdsdev]

Description

Fixes #1261

This PR removes the redundant check that required currentSession.accessToken to exist before allowing a session refresh.

Problem

The refreshSession method was throwing an AuthSessionMissingException when there was no current session, even if a valid refreshToken was provided as a parameter. This blocked a valid use case where you might have a refresh token but no current session.

Solution

• Removed the redundant check for currentSession?.accessToken == null
• The existing null check for the refresh token (currentSessionRefreshToken == null) is sufficient to handle both cases:
  • When a refreshToken parameter is provided
  • When falling back to _currentSession?.refreshToken
• Updated documentation to clarify the behavior
• Improved error message to be more accurate
• Added test to verify the fix works correctly

Changes

• packages/gotrue/lib/src/gotrue_client.dart: Removed redundant check, updated docs
• packages/gotrue/test/client_test.dart: Added test for refreshSession with refreshToken when no current session exists

Testing

• ✅ Added unit test that verifies refreshSession(refreshToken) works when currentSession is null
• ✅ All existing tests should continue to pass (backward compatible)
• ✅ No linter errors

[coveralls]

Pull Request Test Coverage Report for Build 19234218247

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 0 of 1 (0.0%) changed or added relevant line in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.01%) to 79.691%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
packages/gotrue/lib/src/gotrue_client.dart	0	1	0.0%

Files with Coverage Reduction	New Missed Lines	%
packages/gotrue/lib/src/gotrue_client.dart	1	62.02%

Totals
Change from base Build 18568213555:	0.01%
Covered Lines:	3300
Relevant Lines:	4141

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💛 - Coveralls