DocumentViewer: mutex->owner == -1

[nephele]

I realize documentviewer is part of haikuarchives currently and not haiku upstream. Nevertheless I am opening this here because there have been no changes to documentviewer in quite a long time (sadly!) and iirc it worked fine on beta4

For reference, this is the pdf i tried to open: ​https://www.fahr-mit.de/fahr-mit-wAssets/docs/service/downloads/bestellscheine/2022_Bestellformular_Deutschlandticket_V3-noch-keine-TBs.pdf (German transportation form)

~/Desktop>  LD_PRELOAD=libroot_debug.so DocumentViewer 2022_Bestellformular_Deutschlandticket_V3-noch-keine-TBs.pdf 
DocumentViewer: ../haiku-git/src/system/libroot/posix/pthread/pthread_mutex.cpp:95:status_t __pthread_mutex_lock(pthread_mutex_t*, uint32, bigtime_t): mutex->owner == -1
DocumentViewer: ../haiku-git/src/system/libroot/posix/pthread/pthread_mutex.cpp:95:status_t __pthread_mutex_lock(pthread_mutex_t*, uint32, bigtime_t): mutex->owner == -1
Kill Thread

kern: 16943: DEBUGGER: mutex->owner == -1KERN: 16944: DEBUGGER: mutex->owner == -1KERN: debug_server: Thread 16943 entered the debugger: Debugger call: `mutex->owner == -1'KERN: stack trace, current PC 0x4557156a99  </boot/system/lib/libroot_debug.so> _kern_debugger + 0x9:KERN:   (0x7f4228d877d0)  0x4557165fdb  </boot/system/lib/libroot_debug.so> _Z20__pthread_mutex_lockP14_pthread_mutexjl + 0x11b (closest symbol)KERN:   (0x7f4228d87810)  0x198edcb8ab  </boot/system/apps/DocumentViewer> _ZN10BaseEngine4PageEi + 0x5dKERN:   (0x7f4228d87850)  0x198edd8c05  </boot/system/apps/DocumentViewer> _ZN17BasicDocumentView19_SetScrollBarAtPageEi + 0x55KERN:   (0x7f4228d878a0)  0x198edd90c7  </boot/system/apps/DocumentViewer> _ZN17BasicDocumentView9_ShowPageERKi + 0x3fKERN:   (0x7f4228d878c0)  0x198edd90fe  </boot/system/apps/DocumentViewer> _ZN17BasicDocumentView16_ShowCurrentPageEv + 0x26KERN:   (0x7f4228d878e0)  0x198edd6ef6  </boot/system/apps/DocumentViewer> _ZN17BasicDocumentView7SetFileERK7BStringS2_RS0_ + 0x1e0KERN:   (0x7f4228d87950)  0x198edd6705  </boot/system/apps/DocumentViewer> _ZN12DocumentView11FileChangedERK7BStringS2_RS0_ + 0x37KERN:   (0x7f4228d87980)  0x198ede3902  </boot/system/apps/DocumentViewer> _ZN10MainWindow9_OpenFileERK7BStringS2_S0_RKi + 0x96KERN:   (0x7f4228d87a60)  0x198ede3436  </boot/system/apps/DocumentViewer> _ZN10MainWindow15MessageReceivedEP8BMessage + 0x802KERN:   (0x7f4228d87cf0)  0x1814a9e1231  </boot/system/lib/libbe.so> _ZN7BWindow11task_looperEv + 0x1d1KERN:   (0x7f4228d87d80)  0x1814a91d923  </boot/system/lib/libbe.so> _ZN7BLooper7_task0_EPv + 0x23KERN:   (0x7f4228d87da0)  0x4557155809  </boot/system/lib/libroot_debug.so> thread_entry + 0x19

[waddlesplash]

This was a bug in DocumentViewer merely exposed by recent changes. I pushed a fix.