Update current BPM at the end of each loop iteration

With get_current_bpm at the top of this loop iteration, the conditional
was being tested on the old BPM and the new tempo change time.  This
probably wasn't a big deal when the tempo was not changing a lot, but
when it does change a lot, this would create the wrong behavior.  It
should be at the bottom, after the tempo index is updated.  And, with it
here, we don't need to udpate the tempo after we exit the loop.

pretty_midi/pretty_midi.py

@@ -540,8 +540,6 @@ def gt_or_close(a, b):
                 while (tempo_idx < tempo_change_times.shape[0] - 1 and
                         next_beat + beat_remaining*60.0/bpm >=
                         tempo_change_times[tempo_idx + 1]):
-                    # Update the current bpm
-                    bpm = get_current_bpm()
                     # Compute the amount the beat location overshoots
                     overshot_ratio = (tempo_change_times[tempo_idx + 1] -
                                       next_beat)/(60.0/bpm)
@@ -551,8 +549,9 @@ def gt_or_close(a, b):
                     beat_remaining -= overshot_ratio
                     # Increment the tempo index
                     tempo_idx = tempo_idx + 1
-                # Update the current bpm
-                bpm = get_current_bpm()
+                    # Update the current bpm
+                    bpm = get_current_bpm()
+                # Add in the remainder of the beat at the current tempo
                 next_beat += beat_remaining*60./bpm
             # Check if we have just passed the first time signature change
             if self.time_signature_changes and ts_idx == 0: