reader: Remove a panic

The special input functions self-insert, self-insert-not-first, and
and or used to be handled by inputter_t::readch, but they aren't
anymore with `commandline -f`.

I am unsure if these *would* have worked, I can't come up with a use.

So, for now, do nothing instead of panicking.

src/reader.rs

@@ -3172,7 +3172,8 @@ impl ReaderData {
                 self.parser().libdata_mut().is_repaint = false;
             }
             rl::SelfInsert | rl::SelfInsertNotFirst | rl::FuncAnd | rl::FuncOr => {
-                panic!("should have been handled by inputter_t::readch");
+                // This can be reached via `commandline -f and` etc
+                // panic!("should have been handled by inputter_t::readch");
             }
         }
     }

tests/pexpects/bind.py

@@ -375,6 +375,10 @@ expect_prompt("foobar")
 # This should do nothing instead of crash
 sendline("commandline -f backward-jump")
 expect_prompt()
+sendline("commandline -f self-insert")
+expect_prompt()
+sendline("commandline -f and")
+expect_prompt()
 
 # Check that the builtin version of `exit` works
 # (for obvious reasons this MUST BE LAST)