Analyzer fuzz crash: autocompleting malformed import URI

[MichaelRFairhurst]

import "//[/^

Autocomplete at the ^.

Unhandled exception:
server error: {event: server.error, params: {isFatal: false, message: Failed to handle completion domain request: {id: 0, method: completion.getSuggestions, params: {file: /project/bin/test.dart, offset: 12}}, stackTrace: FormatException: Missing end `]` to match `[` in host (at character 3)
//[/
  ^

#0      _Uri._fail (dart:core/uri.dart:1623:5)
#1      _Uri._makeHost (dart:core/uri.dart:1973:9)
#2      new _Uri.notSimple (dart:core/uri.dart:1478:14)
#3      Uri.parse (dart:core/uri.dart:1022:17)
#4      _UriSuggestionBuilder._addFileSuggestions (package:analysis_server/src/services/completion/dart/uri_contributor.dart:155:34)
#5      _UriSuggestionBuilder.visitSimpleStringLiteral (package:analysis_server/src/services/completion/dart/uri_contributor.dart:110:11)
#6      _UriSuggestionBuilder.visitNamespaceDirective (package:analysis_server/src/services/completion/dart/uri_contributor.dart:82:17)
#7      _UriSuggestionBuilder.visitImportDirective (package:analysis_server/src/services/completion/dart/uri_contributor.dart:58:5)
#8      ImportDirectiveImpl.accept (package:analyzer/src/dart/ast/ast.dart:5902:49)
#9      UriContributor.computeSuggestions (package:analysis_server/src/services/completion/dart/uri_contributor.dart:40:35)
<asynchronous suspension>
#10     DartCompletionManager.computeSuggestions (package:analysis_server/src/services/completion/dart/completion_manager.dart:145:31)