Respond to CR.

// FREEBIE

SignalServiceKit/src/Messages/Attachments/TSAttachmentStream.m

@@ -258,10 +258,11 @@ NS_ASSUME_NONNULL_BEGIN
         if (!mediaUrl) {
             return nil;
         }
-        if (![NSData ows_isValidImageAtPath:mediaUrl.path]) {
+        NSData *data = [NSData dataWithContentsOfURL:mediaUrl];
+        if (![data ows_isValidImage]) {
             return nil;
         }
-        return [UIImage imageWithData:[NSData dataWithContentsOfURL:mediaUrl]];
+        return [UIImage imageWithData:data];
     } else {
         return nil;
     }

SignalServiceKit/src/Util/NSData+Image.m

@@ -18,7 +18,7 @@ typedef NS_ENUM(NSInteger, ImageFormat) {
 + (BOOL)ows_isValidImageAtPath:(NSString *)filePath
 {
     NSError *error = nil;
-    NSData *data = [NSData dataWithContentsOfFile:filePath options:NSMappedRead error:&error];
+    NSData *data = [NSData dataWithContentsOfFile:filePath options:NSDataReadingMappedIfSafe error:&error];
     if (error) {
         DDLogError(@"%@ could not read image data: %@", self.tag, error);
     }