ios: Make it easier to play media and record audio simultaneously

close #17
diff --git a/src/ios/CDVSound.m b/src/ios/CDVSound.m
index 0dad4a6..7370026 100644
--- a/src/ios/CDVSound.m
+++ b/src/ios/CDVSound.m
@@ -555,7 +555,10 @@
             }
             // get the audioSession and set the category to allow recording when device is locked or ring/silent switch engaged
             if ([self hasAudioSession]) {
-                [self.avSession setCategory:AVAudioSessionCategoryRecord error:nil];
+                if (![self.avSession.category isEqualToString:AVAudioSessionCategoryPlayAndRecord]) {
+                    [self.avSession setCategory:AVAudioSessionCategoryRecord error:nil];
+                }
+
                 if (![self.avSession setActive:YES error:&error]) {
                     // other audio with higher priority that does not allow mixing could cause this to fail
                     errorMsg = [NSString stringWithFormat:@"Unable to record audio: %@", [error localizedFailureReason]];