D9987: Lessen log spam by not checking for existence of file with empty name

[Henrik Fehlauer]

rkflx created this revision.
rkflx added a reviewer: Frameworks.
Restricted Application added a project: Frameworks.
rkflx requested review of this revision.

REVISION SUMMARY
  Calls to `QFile::exists()` while starting a Plasma session
  resulted in `Empty filename passed to function` being logged
  since Qt 5.10 (0dee566e98f5 in qtbase).
  
  This can be avoided by skipping the check for empty filenames, which
  would have returned `false` in any case. Similarly to what was done in
  https://phabricator.kde.org/R241:549fc81e8e8a47afc5621d1383de5d440fc35f76, also port to the faster `QFileInfo::exists()`.
  
  Note this does not simply hide a deeper issue, i.e. the actual cause
  resulting in the empty variable, because `libpath.isEmpty()` will be
  handled explicitly later on. In the case under investigation
  `/usr/lib64/libexec/org_kde_powerdevil` did not match
  `/usr/lib64/libexec/kf5`, but even if it was in that subfolder there
  would have been no corresponding `libkdeinit5_` anyway.
  
  CCBUG: 388611

TEST PLAN
  Grep session log for "Empty filename passed to function" after
  restarting the Plasma session and compare before/after.

REPOSITORY
  R303 KInit

BRANCH
  master

REVISION DETAIL
  https://phabricator.kde.org/D9987

AFFECTED FILES
  src/kdeinit/kinit.cpp

To: rkflx, #frameworks
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