Add time buffer for routes that don't start on time

[moshobo]

Problem

Currently, if there are no active routes at the start of the output GIF, the simulation will just start showing the first route available. For example, a train that leaves at 4:33pm and the simulation runs from 4:00-5:00pm. Instead of simulating 33 minutes of "buffer", the simulated train will depart at 4:00pm as the simulation starts

Solution

There should be some sort of "time buffer" so that a route only begins at the correct frame in the simulation

Workarounds

The current workaround is to add additional transit routes that are active before and through the start of the animation, but that isn't really a good solution...

[moshobo]

I think the issue is that this line of code only updates the lon/lat values if there are values for that time frame. There needs to be another bit of code that inserts an empty/None value if there is no transit vehicles to plot for any given time frame

for time in times:
    matching_rows = filtered_route_loc[filtered_route_loc['time'] == time]
    
    if not matching_rows.empty:
        lon_values = matching_rows['lon'].tolist()
        lat_values = matching_rows['lat'].tolist()

        x_trip.append(lon_values)
        y_trip.append(lat_values)