LibLine: Handle interrupts again

This commit makes LibLine handle interrupts (as reported via
interrupted() and resized()) again.
There is a little catch with the shell:
```
$     ls |
pipe> <C-c> (prompt stays here until a key is pressed)
```

Shell/main.cpp

@@ -133,7 +133,7 @@ int main(int argc, char** argv)
     }
 
     editor->on_interrupt_handled = [&] {
-        if (!shell->should_read_more()) {
+        if (shell->should_read_more()) {
             shell->finish_command();
             editor->finish();
         }