Remove unavailable registers from the register view

Co-authored-by: Andrea Cardaci <[email protected]>

Author: N00byEdge

.gdbinit

@@ -1960,6 +1960,9 @@ class Registers(Dashboard.Module):
                 continue
             value = gdb.parse_and_eval('${}'.format(name))
             string_value = Registers.format_value(value)
+            # exclude unavailable registers (see #255)
+            if string_value == '<unavailable>':
+                continue
             changed = self.table and (self.table.get(name, '') != string_value)
             self.table[name] = string_value
             registers.append((name, string_value, changed))