[fix] avoid segfault in case of missing mountpoint

[mizhka]

Simple fix to avoid segfault in DirReadJob::shouldCrossIntoFilesystem in logging logic

[shundhammer]

Thank you. I shifted the code a bit around, though.

But I am curious: Did you actually get a segfault? Of course it's always safer (and strongly advised) to check the result of any operation that can return a null pointer, and I hope that I did that everywhere else in QDirStat; but under what circumstances does it actually get to this code if that URL isn't actually a mount point? It might still legitimately happen, but when and how?

[mizhka]

Yes, on FreeBSD there is no found mountpoint for /net, /dev and /proc.
Test case is to run scan for root path with cross-mount check.
Also last commit should be adjusted:

if ( mountPoint ) => if ( ! mountPoint )

Actual backtrace (before adjustment mentioned above) :

(lldb) thread backtrace
* thread #1, name = 'qdirstat', stop reason = signal SIGSEGV
  * frame #0: 0x0000000825d151ba libQt5Core.so.5`QString::indexOf(QString const&, int, Qt::CaseSensitivity) const [inlined] QString::unicode(this=0x0000000000000008) const at qstring.h:1080:41
    frame #1: 0x0000000825d151ba libQt5Core.so.5`QString::indexOf(this=0x0000000000000008, str=0x0000000820432ca8, from=0, cs=CaseSensitive) const at qstring.cpp:3764:50
    frame #2: 0x00000000002a8225 qdirstat`QString::contains(this=0x0000000000000008, s=0x0000000820432ca8, cs=CaseSensitive) const at qstring.h:1358:10
    frame #3: 0x00000000003905a5 qdirstat`QDirStat::MountPoint::isSystemMount(this=0x0000000000000000) const at MountPoints.cpp:106:20
    frame #4: 0x00000000002d1021 qdirstat`QDirStat::DirReadJob::shouldCrossIntoFilesystem(this=0x000000083afa6f80, dir=0x000000086c56c100) const at DirReadJob.cpp:182:16
    frame #5: 0x00000000002d27a3 qdirstat`QDirStat::LocalDirReadJob::processSubDir(this=0x000000083afa6f80, entryName=0x0000000820433078, subDir=0x000000086c56c100) at DirReadJob.cpp:421:40
    frame #6: 0x00000000002d1c21 qdirstat`QDirStat::LocalDirReadJob::startReading(this=0x000000083afa6f80) at DirReadJob.cpp:290:7

[shundhammer]

Yes, on FreeBSD there is no found mountpoint for /net, /dev and /proc. Test case is to run scan for root path with cross-mount check.

OK, I see. Thanks for clarifying.

Also last commit should be adjusted:

if ( mountPoint ) => if ( ! mountPoint )

Duh. You are right, of course. I was too hasty. ;-(

Fixed.