[WARP] to_bn_calling_convention panics when `BNGetArchitectureDefaultCallingConvention` returns None

[sentry]

Sentry Issue: BINARYNINJA-82

SIGABRT / SI_TKILL / 0x0: Fatal Error: SIGABRT / SI_TKILL / 0x0
  File "mod.rs", line 368, in std::sys::pal::unix::abort_internal
  File "process.rs", line 2500, in std::process::abort
  File "rt.rs", line 57, in __rustc::rust_panic
  File "panicking.rs", line 859, in std::panicking::panic_with_hook
  File "panicking.rs", line 700, in std::panicking::panic_handler::{{closure}}
...
(42 additional frame(s) were not displayed)

@bdash says:

See

binaryninja-api/plugins/warp/src/convert/types.rs

Lines 274 to 284 in f1a688a

	pub fn to_bn_calling_convention<A: BNArchitecture>(
	arch: &A,
	calling_convention: &CallingConvention,
	) -> BNRef<BNCallingConvention> {
	for cc in &arch.calling_conventions() {
	if cc.name().as_str() == calling_convention.name {
	return cc.clone();
	}
	}
	arch.get_default_calling_convention().unwrap()
	}

. I'm not sure under what conditions this can happen.