python: handle invalid argument (zero) for reg_name() & insn_name() of class CsInsn

bindings/python/capstone/__init__.py

@@ -502,6 +502,9 @@ class CsInsn(object):
             # Diet engine cannot provide register name
             raise CsError(CS_ERR_DIET)
 
+        if reg_id == 0:
+            return "(invalid)"
+
         return _cs.cs_reg_name(self._cs.csh, reg_id).decode('ascii')
 
     # get the instruction string
@@ -510,6 +513,9 @@ class CsInsn(object):
             # Diet engine cannot provide instruction name
             raise CsError(CS_ERR_DIET)
 
+        if self._raw.id == 0:
+            return "(invalid)"
+
         return _cs.cs_insn_name(self._cs.csh, self.id).decode('ascii')
 
     # verify if this insn belong to group with id as @group_id