Treat empty crashData the same as missing crashData
Treat empty crashData the same as missing crashData

This is needed for consistency between client and server, because the server's database stores the empty string rather than None. The same fix was applied for ASan a long time ago.

MozillaSecurity/FuzzManager,MozillaSecurity/FuzzManager,MozillaSecurity/FuzzManager,MozillaSecurity/FuzzManager