Patch _fs_gs_helper when debugging windows remotely (#2478)

* move remote check earlier

* move remote check earlier

* add try except if register does not exist

* check if register eists before trying to fetch

* moved register check to only x86-64

* use .find() to determine wether register exists

pwndbg/gdblib/regs.py

@@ -32,6 +32,13 @@ from pwndbg.lib.regs import RegisterSet
 from pwndbg.lib.regs import reg_sets
 
 
+@pwndbg.gdblib.proc.OnlyWhenRunning
+def register_exists(register_name: str, frame: gdb.Frame | None = None) -> bool:
+    if frame is None:
+        frame = gdb.selected_frame()
+    return bool(frame.architecture().registers().find(register_name))
+
+
 @pwndbg.gdblib.proc.OnlyWhenRunning
 def gdb_get_register(name: str, frame: gdb.Frame | None = None) -> gdb.Value | None:
     if frame is None:
@@ -247,6 +254,8 @@ class module(ModuleType):
         Requires ptrace'ing the child directory if i386."""
 
         if pwndbg.aglib.arch.name == "x86-64":
+            if not register_exists(regname):
+                return 0
             reg_value = gdb_get_register(regname)
             return int(reg_value) if reg_value is not None else 0