Don't assume the working directory exists.

Author: asbjornu

src/GitVersionCore/Helpers/ProcessHelper.cs

@@ -50,11 +50,18 @@ public static int Run(Action<string> output, Action<string> errorOutput, TextRea
         {
             if (String.IsNullOrEmpty(exe))
                 throw new ArgumentNullException("exe");
+            
             if (output == null)
                 throw new ArgumentNullException("output");
 
             workingDirectory = workingDirectory ?? Environment.CurrentDirectory;
 
+            if (!Directory.Exists(workingDirectory))
+            {
+                errorOutput(string.Format("The directory {0} doesn't exist.", workingDirectory));
+                return 1;
+            }
+
             var psi = new ProcessStartInfo
             {
                 UseShellExecute = false,