prr#44 prr crashes if only one line in the commit message (#45)

Reviewed by: Dan McDonald <danmcd@kebe.com>

Author: bahamat

.gitmodules

@@ -1,3 +1,3 @@
 [submodule "deps/eng"]
 	path = deps/eng
-	url = https://github.com/joyent/eng
+	url = https://github.com/TritonDataCenter/eng

deps/eng

@@ -7,6 +7,7 @@
 
 /*
  * Copyright 2020 Joyent, Inc.
+ * Copyright 2022 MNX Cloud, Inc.
  */
 
 /*
@@ -530,8 +531,10 @@ function writeCommitMessage(args, cb) {
                 remaining_messages = remaining_messages.slice(1);
             }
 
-            while (remaining_messages[0].trim() === '') {
-                remaining_messages = remaining_messages.slice(1);
+            if (remaining_messages.length > 0) {
+                while (remaining_messages[0].trim() === '') {
+                    remaining_messages = remaining_messages.slice(1);
+                }
             }
 
             fs.writeSync(info.fd, format(