Check if the "lib" directory exists before iterating its sub-tree (#196)

* Check if the "lib" directory exists before iterating its sub-tree

* bump flutter version to 3.24.3

.fvmrc

@@ -1,4 +1,4 @@
 {
-  "flutter": "3.22.2",
+  "flutter": "3.24.3",
   "flavors": {}
 }

lib/src/analyze/package_api_analyzer.dart

@@ -384,6 +384,9 @@ class PackageApiAnalyzer {
 
   Iterable<_FileToAnalyzeEntry> _findPublicFilesInProject(
       String normalizedAbsolutePath) {
+    if (!Directory(normalizedAbsolutePath).existsSync()) {
+      return [];
+    }
     final srcPath = path.join(normalizedAbsolutePath, 'src');
     return Directory(normalizedAbsolutePath)
         // if we want to consider all files that are not in the src folder as potential entry points