sentry_set_user() crashes when called after sentry_init()

[matok]

Important details

• Saas (sentry.io)
• mac (10.15)
• built from release 0.1.2
• sentry with crashpad backend

Description

Invoking sentry_set_user() before sentry_init() works fine, all following events are tagged with provided user details, but when it's called after sentry_init, it crashes on BAD_ACCESS because of NULL FILE* pointer writer->context in mpack_file_writer_flush.

I don't know whether this is an expected behaviour, but it would be nice if we could change user details after initialization.

[matok]

I just compiled the same code on windows, also with crashpad backend and it doesn't crash.

[mitsuhiko]

This might be the same core issues as #84. It fails to open the event file. I'm adding a fix for the crash in but it won't make the user data show up yet.