Fix signature help panic when too large (#4030)

When signature help is too large it may cause a panic when it is too
large, now I just make the hover do an intersection with surface to make
sure it never overflow.

helix-term/src/ui/lsp.rs

@@ -68,8 +68,9 @@ impl Component for SignatureHelp {
 
         let (_, sig_text_height) = crate::ui::text::required_size(&sig_text, area.width);
         let sig_text_area = area.clip_top(1).with_height(sig_text_height);
+        let sig_text_area = sig_text_area.inner(&margin).intersection(surface.area);
         let sig_text_para = Paragraph::new(sig_text).wrap(Wrap { trim: false });
-        sig_text_para.render(sig_text_area.inner(&margin), surface);
+        sig_text_para.render(sig_text_area, surface);
 
         if self.signature_doc.is_none() {
             return;