To reproduce:
1. Open Search pane (Ctrl + Shift + F)
2. Scope: "Find in File System"
3. SearchEngine: "Silver Searcher"
4. Directory : Point into your home dir
5. Search for: "a"
6. Press "Search"
7. Wait about 10 - 15 seconds for a crash

The Qt assert is being issued on the crash:

ASSERT: "len >= 0" in file /home/jarek/dev/qt-64/qtbase/src/corelib/text/qbytearrayview.h, line 137

Update: It looks like the data size reported by the Process is bigger than 2.5 GB, and the crash happens in: QTextCodec::toUnicode() when calling Process::stdOut().