Merge branch 'jn/CHT-1416-Protect-against-init-NSString-with-null-str…

…ing-in-MEGAChatMessage_7_3_0' into 'release/v7.3.0'

CHT-1416: Protect against init NSString with null string in MEGAChatMessage

See merge request megachat/MEGAchat!2040

bindings/Objective-C/MEGAChatMessage.mm

@@ -176,11 +176,15 @@ - (uint64_t)userHandleAtIndex:(NSUInteger)index {
 }
 
 - (NSString *)userNameAtIndex:(NSUInteger)index {
-    return self.megaChatMessage ? [[NSString alloc] initWithUTF8String:self.megaChatMessage->getUserName((unsigned int)index)] : nil;
+    if (!self.megaChatMessage) return nil;
+    const char *ret = self.megaChatMessage->getUserName((unsigned int)index);
+    return ret ? [[NSString alloc] initWithUTF8String:ret] : nil;
 }
 
 - (NSString *)userEmailAtIndex:(NSUInteger)index {
-    return self.megaChatMessage ? [[NSString alloc] initWithUTF8String:self.megaChatMessage->getUserEmail((unsigned int)index)] : nil;
+    if (!self.megaChatMessage) return nil;
+    const char *ret = self.megaChatMessage->getUserEmail((unsigned int)index);
+    return ret ? [[NSString alloc] initWithUTF8String:ret] : nil;
 }
 
 - (BOOL)hasScheduledMeetingChangeForType:(MEGAChatMessageScheduledMeetingChangeType)changeType {