Catch exceptions when importing from search paths (microsoft#525)

* catch exceptions when importing from search paths

* retry instead of not found

Author: jakebailey

src/Analysis/Engine/Impl/Interpreter/Ast/AstModuleResolution.cs

@@ -205,6 +205,12 @@ public async Task<TryImportModuleResult> TryImportModuleAsync(string name, PathR
                 } catch (OperationCanceledException) {
                     _log?.Log(TraceLevel.Error, "ImportTimeout", name, "ImportFromSearchPaths");
                     return TryImportModuleResult.Timeout;
+                } catch (Exception ex) when (
+                    ex is IOException // FileNotFoundException, DirectoryNotFoundException, PathTooLongException, etc 
+                    || ex is UnauthorizedAccessException
+                ) {
+                    _log?.Log(TraceLevel.Error, "ImportException", name, "ImportFromSearchPaths", ex.GetType().Name, ex.Message);
+                    return TryImportModuleResult.NeedRetry;
                 }
             }