Fix capturing of registers in ErrorHandler
Back in RISCOS_Lib 5.35, a bug was introduced in ErrorHandler where it would try saving the registers to a garbage address for SCL builds where SASTMhatbroken is false. This bug has gone unnoticed until now because up until a few months ago, SASTMhatbroken was always true (commit 3b7d39bd in RISCOS_Lib 6.13).
Move the offending line of code out of the SASTMhatbroken block so that register capturing will work correctly for all build configs.
Fixes issue reported on the forums (tested with a ROM build on Pi 4): https://www.riscosopen.org/forum/forums/4/topics/17647