Attempt to verify tput exists before using it

src/functions.php

@@ -10,6 +10,17 @@ use Aviat\Kilo\Enum\{
 	Highlight,
 };
 
+/**
+ * See if tput exists for fallback terminal size detection
+ *
+ * @return bool
+ * @codeCoverageIgnore
+ */
+function has_tput(): bool
+{
+	return shell_exec('type tput') === 0;
+}
+
 // ----------------------------------------------------------------------------
 // ! Terminal size
 // ----------------------------------------------------------------------------
@@ -28,6 +39,8 @@ function get_window_size(): array
 	$res = $ffi->ioctl(C::STDOUT_FILENO, C::TIOCGWINSZ, FFI::addr($ws));
 
 	if ($res === -1 || $ws->ws_col === 0)
+	{
+		if (has_tput())
 		{
 			$rows = trim(shell_exec('tput lines'));
 			$cols = trim(shell_exec('tput cols'));
@@ -35,6 +48,10 @@ function get_window_size(): array
 			return [(int)$rows, (int)$cols];
 		}
 
+		// Worst-case, return an arbitrary 'standard' size
+		return [80, 25];
+	}
+
 	return [$ws->ws_row, $ws->ws_col];
 }
 
@@ -110,7 +127,7 @@ function is_digit(string $char): bool
  */
 function is_space(string $char): bool
 {
-	$ws = [' ', "\t", "\n", "\r", "\xa", "\xb", "\xc"];
+	$ws = [' ', "\t", "\n", "\r", "\v", "\f"];
 	return is_ascii($char) && in_array($char, $ws, TRUE);
 }