lib: ignore VS instances that cause COMExceptions

I have quite a few instances of VS installed and it looks like
Find-VisualStudio.cs enumerates all of them, even when
find-visualstudio.js already knows which one it wants (from the
environment variable in the developer command prompt).  One of them
(from 15.7.2, if that's interesting) causes a COMException on the
ISetupInstance2.GetPackages call.  Ignoring such packages seems
harmless and unblocks the rest of the run.

PR-URL: #2018
Reviewed-By: João Reis <reis@janeasystems.com>

lib/Find-VisualStudio.cs

@@ -205,7 +205,14 @@ public static void PrintJson()
                     return;
                 }
 
-                instances.Add(InstanceJson(rgelt[0]));
+                try
+                {
+                    instances.Add(InstanceJson(rgelt[0]));
+                }
+                catch (COMException)
+                {
+                    // Ignore instances that can't be queried.
+                }
             }
         }