Fixed exception in VH when a manifest has no aliases.

In cases where a manifest has no aliases the aliases set lookup
in FindAndReadManifestsByPackageName() would throw an exception.
This fixes the issue by adding an empty set of aliases for manifests
with no aliases.

Change-Id: I5c459bb092666088c3eedb33155bf06df75b6285

Author: Stewart Miles

source/VersionHandlerImpl/src/VersionHandlerImpl.cs

@@ -1383,7 +1383,7 @@ private static KeyValuePair<string, int> FindHighestPriorityManifestName(
             if (depth > maxDepth) {
                 Log(String.Format(
                         "Detected manifest name alias loop for name {0}, to fix this change the " +
-                        "list (see below) to not contain a loop:\n{1}" +
+                        "list (see below) to not contain a loop:\n{1}",
                         name, String.Join("\n", (new List<string>(aliasesByName.Keys)).ToArray())),
                     level: LogLevel.Warning);
                 return new KeyValuePair<string, int>(name, -1);
@@ -1429,6 +1429,10 @@ private Dictionary<string, HashSet<string>> GetManifestAliasesByName() {
                         }
                         aliases.Add(metadata.customManifestNames.Values[0]);
                     }
+                    // If there are no aliases, store an empty set.
+                    if (metadata.customManifestNames.Values.Count == 0) {
+                        aliasesByName[metadata.ManifestName] = new HashSet<string>();
+                    }
                 }
             }
             // Display adjacency list for debugging.