Fix bugs in the log viewer

pkg/analysis_server/tool/instrumentation/page/log_page.dart

Index: pkg/analysis_server/tool/instrumentation/page/log_page.dart
diff --git a/pkg/analysis_server/tool/instrumentation/page/log_page.dart b/pkg/analysis_server/tool/instrumentation/page/log_page.dart
index ad1194d3f8eac349d1b0605dedcae80c9f52df29..756b2f4a9f157c0fccfaa503b957433720bc8322 100644
--- a/pkg/analysis_server/tool/instrumentation/page/log_page.dart
+++ b/pkg/analysis_server/tool/instrumentation/page/log_page.dart
@@ -225,7 +225,11 @@ function selectEntryGroup(pageStart) {
       sink.writeln('</option>');
     }
     sink.writeln('</select>');
-    sink.writeln('Events $pageStart - ${pageEnd - 1} of ${length - 1}');
+    if (length == 0) {
+      sink.writeln('No matching events');
+    } else {
+      sink.writeln('Events $pageStart - ${pageEnd - 1} of $length');
+    }
     sink.writeln('</div>');
 
     sink.writeln('<div style="float: right">');