[License] Enable empty_catches lint

engine/src/flutter/tools/licenses/analysis_options.yaml

@@ -16,6 +16,7 @@ linter:
     - close_sinks
     - control_flow_in_finally
     - empty_statements
+    - empty_catches
     - hash_and_equals
     # - invariant_booleans  # Produces false positives, see https://github.com/flutter/flutter/issues/5790
     - iterable_contains_unrelated_type

engine/src/flutter/tools/licenses/lib/filesystem.dart

@@ -332,6 +332,8 @@ mixin Latin1TextFile implements TextFile {
         cache(UTF8Of(this), () => utf8.decode(readBytes()));
         isUTF8 = true;
       } on FormatException {
+        // Exceptions are fine/expected for non-UTF8 text, which we test for
+        // immediately below.
       }
       if (isUTF8)
         throw '$fullName contains valid UTF-8 and is probably not actually encoded as Win1252';

engine/src/flutter/tools/licenses/lib/licenses.dart

@@ -327,19 +327,19 @@ abstract class License implements Comparable<License> {
     try {
       latin1Encoded = latin1.encode(body);
       isUTF8 = false;
-    } on ArgumentError { }
+    } on ArgumentError { /* Fall through to next encoding check. */ }
     if (!isUTF8) {
       bool isAscii = false;
       try {
         ascii.decode(latin1Encoded);
         isAscii = true;
-      } on FormatException { }
+      } on FormatException { /* Fall through to next encoding check */ }
       if (isAscii)
         return;
       try {
         utf8.decode(latin1Encoded);
         isUTF8 = true;
-      } on FormatException { }
+      } on FormatException { /* We check isUTF8 below and throw if necessary */ }
       if (isUTF8)
         throw 'tried to create a License object with text that appears to have been misdecoded as Latin1 instead of as UTF-8:\n$body';
     }