Fix signed versus unsigned comparison.
https://bugs.launchpad.net/libvterm/+bug/1668780

Patch updated to apply on:
https://github.com/neovim/libvterm/tree/nvim

Index: bin/vterm-ctrl.c
--- bin/vterm-ctrl.c.orig
+++ bin/vterm-ctrl.c
@@ -79,9 +79,9 @@ static bool seticanon(bool icanon, bool echo)
   return ret;
 }
 
-static void await_c1(unsigned char c1)
+static void await_c1(int c1)
 {
-  unsigned char c;
+  int c;
 
   /* await CSI - 8bit or 2byte 7bit form */
   bool in_esc = false;
@@ -106,7 +106,7 @@ static char *read_csi()
   char csi[32];
   int i = 0;
   for(; i < sizeof(csi)-1; i++) {
-    char c = csi[i] = getchar();
+    int c = csi[i] = getchar();
     if(c >= 0x40 && c <= 0x7e)
       break;
   }
@@ -125,7 +125,7 @@ static char *read_dcs()
   bool in_esc = false;
   int i = 0;
   for(; i < sizeof(dcs)-1; ) {
-    char c = getchar();
+    int c = getchar();
     if(c == 0x9c) // ST
       break;
     if(in_esc && c == 0x5c)
