Fix Google Groupware segfault

If m_account is null, the code tried to call m_account->accountName().
This could happen when clicking "Configure" in the settings dialog.
1 job for v20.12.0 in 15 minutes and 52 seconds (queued for 264 minutes and 44 seconds)
latest
Status Job ID Name Coverage
  Build
failed #81976
build_clazy_clang_tidy

00:15:52

 
Name Stage Failure
failed
build_clazy_clang_tidy Build
[ 92%] Linking CXX executable ../../bin/akonadi_imap_resource
[ 92%] Built target akonadi_imap_resource
make: *** [Makefile:160: all] Error 2
Uploading artifacts for failed job
Uploading artifacts...
WARNING: JUnitTestResults.xml: no matching files
ERROR: No files to upload
Cleaning up file based variables
ERROR: Job failed: exit code 1