determine delay based on samples, not seconds (#229)

Author: Brendonovich

src/software/resampling/context.rs

@@ -149,12 +149,7 @@ impl Context {
 
     /// Get the remaining delay.
     pub fn delay(&self) -> Option<Delay> {
-        unsafe {
-            match swr_get_delay(self.as_ptr() as *mut _, 1) {
-                0 => None,
-                _ => Some(Delay::from(self)),
-            }
-        }
+        unsafe { Some(Delay::from(self)).filter(|d| d.output > 0) }
     }
 
     /// Run the resampler from the given input to the given output.