Bug fix: Cannot modify immutable list

[ahsanirfan961]

I encountered this bug,

════════ Exception caught by widgets library ═══════════════════════════════════
The following UnsupportedError was thrown building MapLocationSelectWidget(dependencies: [InheritedCupertinoTheme, _InheritedTheme, _LocalizationsScope-[GlobalKey#50ace]], state: _MapLocationSelectWidgetState#fc789):
Unsupported operation: Cannot clear an unmodifiable list

The relevant error-causing widget was:
MapLocationSelectWidget MapLocationSelectWidget:file:///D:/Ahsan/Job/Point-of-Sale-Project/frontend/lib/components/widgets/form/address_field.dart:85:9

When the exception was thrown, this was the stack:
#0 UnmodifiableListMixin.clear (dart:_internal/list.dart:157:5)
list.dart:157
#1 _SearchFieldState.didUpdateWidget (package:searchfield/src/searchfield.dart:711:22)

Can't modify immutable list. So I replaced filteredResult.clear() with filteredResult = [].

Pre-launch Checklist

• [ ] I read the Contributor Guide and followed the process outlined there for submitting PRs.
• [x] I listed at least one issue that this PR fixes in the description above.
• [ ] I updated/added relevant documentation (doc comments with ///).
• [ ] I added new tests to check the change I am making, or this PR is [test-exempt].
• [ ] All existing and new tests are passing using flutter test

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