Crash when receiving a new mail

[nicodh]

During my tests with desktop I sent many mails from Android to test the behaviour. Suddenly (and not reproducable) I had a crash in dc core.

Here the log output created by rust core:

name = 'deltachat_ffi'
operating_system = 'unix:OSX'
crate_version = '1.0.0-alpha.0'
explanation = '''
Panic occurred in file 'src/libcore/option.rs' at line 1036
'''
method = 'Panic'
backtrace = '''
stack backtrace:
0: (0x10cbabe2e)
1: backtrace::capture::Backtrace::new::h2204ad1c961592ba (0x10cba9f38)
2: (0x10ca82927)
3: human_panic::handle_dump::h5f922b565301d3e1 (0x10ca8559d)
4: (0x10c29d87b)
5: std::panicking::rust_panic_with_hook::h8a88400b135e8531 (0x10cbd94b1)
6: (0x10cbd8efd)
7: _rust_begin_unwind (0x10cbd8de9)
8: core::panicking::panic_fmt::h2cfc694e6c2ca870 (0x10cc03f42)
9: core::option::expect_failed::hfa98a0848680c06f (0x10cc0405e)
10: (0x10c30aa9c)
11: deltachat::imap::Imap::fetch::hbab7a9793ea63282 (0x10c305c4e)
12: deltachat::dc_job::dc_perform_imap_fetch::h0f133c7f0a62f38e (0x10c2c6c58)
13: _dc_perform_imap_fetch (0x10c29dcee)
14: (0x10c29520a)
15: __pthread_body (0x7fff92c0693b)
16: __pthread_body (0x7fff92c06887)'''

and the Electron report:

Thread 33 Crashed:
0 libsystem_kernel.dylib 0x00007fff92b1bd42 __pthread_kill + 10
1 libsystem_pthread.dylib 0x00007fff92c09457 pthread_kill + 90
2 libsystem_c.dylib 0x00007fff92a81420 abort + 129
3 node.napi.node 0x000000010cbe7fd9 0x10c28f000 + 9801689
4 node.napi.node 0x000000010cbd7090 0x10c28f000 + 9732240
5 node.napi.node 0x000000010cbd9623 rust_panic + 99
6 node.napi.node 0x000000010cbd94fa std::panicking::rust_panic_with_hook::h8a88400b135e8531 + 666
7 node.napi.node 0x000000010cbd8efd 0x10c28f000 + 9740029
8 node.napi.node 0x000000010cbd8de9 rust_begin_unwind + 9
9 node.napi.node 0x000000010cc03f42 core::panicking::panic_fmt::h2cfc694e6c2ca870 + 66
10 node.napi.node 0x000000010cc0405e core::option::expect_failed::hfa98a0848680c06f + 94
11 node.napi.node 0x000000010c30aa9c 0x10c28f000 + 506524
12 node.napi.node 0x000000010c305c4e deltachat::imap::Imap::fetch::hbab7a9793ea63282 + 318
13 node.napi.node 0x000000010c2c6c58 deltachat::dc_job::dc_perform_imap_fetch::h0f133c7f0a62f38e + 344
14 node.napi.node 0x000000010c29dcee dc_perform_imap_fetch + 14
15 node.napi.node 0x000000010c29520a 0x10c28f000 + 25098
16 libsystem_pthread.dylib 0x00007fff92c0693b _pthread_body + 180
17 libsystem_pthread.dylib 0x00007fff92c06887 _pthread_start + 286
18 libsystem_pthread.dylib 0x00007fff92c0608d thread_start + 13