gdb: z80: guard saved_reg addr access

The z80 unwinder calls trad_frame_saved_reg::addr() on entries that
are still REALREG, which trips an assertion in debug builds. Guard the
addr() access with is_addr() so only actual saved-address regs are
adjusted. This keeps debug and release behavior consistent.

Author: adriweb

gdb/z80-tdep.c

@@ -641,7 +641,7 @@ z80_frame_unwind_cache (const frame_info_ptr &this_frame,
   /* Adjust all the saved registers so that they contain addresses and not
      offsets.  */
   for (i = 0; i < gdbarch_num_regs (gdbarch) - 1; i++)
-    if (info->saved_regs[i].addr () > 0)
+    if (info->saved_regs[i].is_addr () && info->saved_regs[i].addr () > 0)
       info->saved_regs[i].set_addr
 	(info->prev_sp - info->saved_regs[i].addr () * addr_len);