MIPS: Support orphaned lo16 relocs. Fixes #627

[bmourit]

MIPS: Add support for orphaned lo16 relocations.

This fixes issue #627

[bmourit]

The actual issue here is on line 794:
if (lastMipsHi16 == nullptr) return;

The lo16 could technically still be processed without any hi16 value at all. While this patch does fix the issue, it does so by storing info that is technically unneeded.
In the end, however, this is probably the simplest solution, as any other would likely require even more additional code to handle this 1 specific case.

[PeterMatula]

Looks ok, lets Run TeamCity builds.

[PeterMatula]

Well, some regression tests in TeamCity builds failed, but this is due to changes in regression tests suite and RetDec master branch - these repos changed, but changes were not merged to this PR. So this is probably nothing to worry about.

[PeterMatula]

Manually tested - it is ok.