Fix UB in defaults loading (#5456)

* Fix UB in defaults loading

* Add changelog entry

* One more isDirectory

Co-authored-by: samedson <samedson@google.com>

Author: morganchen12

Crashlytics/CHANGELOG.md

@@ -1,6 +1,7 @@
 # Unreleased
 
 - [fixed] Fixed unchecked `malloc`s in Crashlytics (#5428).
+- [fixed] Fixed an instance of undefined behavior when loading files from disk (#5454).
 
 # v4.0.0
 

Crashlytics/Crashlytics/FIRCLSUserDefaults/FIRCLSUserDefaults.m

@@ -235,7 +235,7 @@ - (void)synchronize {
   NSDictionary *state = [self dictionaryRepresentation];
   dispatch_sync(self.synchronizationQueue, ^{
 #if CLS_TARGET_CAN_WRITE_TO_DISK
-    BOOL isDirectory;
+    BOOL isDirectory = NO;
     BOOL pathExists = [[NSFileManager defaultManager] fileExistsAtPath:[self->_directoryURL path]
                                                            isDirectory:&isDirectory];
 
@@ -280,7 +280,7 @@ - (NSDictionary *)loadDefaults {
   __block NSDictionary *state = nil;
   dispatch_sync(self.synchronizationQueue, ^{
 #if CLS_TARGET_CAN_WRITE_TO_DISK
-    BOOL isDirectory;
+    BOOL isDirectory = NO;
     BOOL fileExists = [[NSFileManager defaultManager] fileExistsAtPath:[self->_fileURL path]
                                                            isDirectory:&isDirectory];
 
@@ -289,7 +289,7 @@ - (NSDictionary *)loadDefaults {
       if (nil == state) {
         FIRCLSErrorLog(@"Failed to read existing UserDefaults file");
       }
-    } else if (!fileExists && !isDirectory) {
+    } else if (!fileExists) {
       // No file found. This is expected on first launch.
     } else if (fileExists && isDirectory) {
       FIRCLSErrorLog(@"Found directory where file expected. Removing conflicting directory");