Crash when calling hiddbgIsHdlsVirtualDeviceAttached()

[cathery]

Was having some trouble getting Hdls to work, I was doing everything correctly but it would always crash when calling e.g. hiddbgIsHdlsVirtualDeviceAttached().

After a bit of debugging I realized the function tries to access g_hiddbgHdlsTmem.src_addr where src_addr is NULL.
This wasn't a problem before, but the PR #601 switched from using tmemCreate to tmemCreateFromMemory to initalize g_hiddbgHdlsTmem, which seems to have thrown a wrench into things.

After I changed tmemCreateFromMemory to properly initialize t->src_addr, everything started working again.

tmem.c(52):

-    t->src_addr = NULL;
+    t->src_addr = buf;

[fincs]

t->src_addr is only non-NULL when the TransferMemory object owns its memory. tmemCreateFromMemory is used to create a TransferMemory object which does not own its memory. hiddbgIsHdlsVirtualDeviceAttached should probably be fixed to not rely on reading src_addr.