Fix negative total XP calculation when skill starts

Closes #1734

Summary:
If you start a skill like fishing lobster after logging in,
you will have the xpGained value as `90`.
But, since you just started the skill, it will divide by `0`.
This results in the max integer value of `2147483647`.

If you did fletching before fishing, and had a XP per hour of `40000`.
Then when you add the fishing XP per hour of `2147483647`, the
result overflows and you get a negative number as the total XP per hour.

Solution:
Don't divide by zero, instead suppose that the skill has been active
for **at least** 60 seconds. This will result in a fair estimate that
improves as the skill continues to be used, rather than the ridiculous
estimate of 2 Billion one second and 200K the next second.

60 seconds is chosen over 1 or 5 or 10 seconds as the result is more
conservative and closer matches my hourly XP experiences.

runelite-client/src/main/java/net/runelite/client/plugins/xptracker/XpStateSingle.java

@@ -71,7 +71,11 @@ class XpStateSingle
 			return 0;
 		}
 
-		long timeElapsedInSeconds = Duration.between(skillTimeStart, Instant.now()).getSeconds();
+		// If the skill started just now, we can divide by near zero, this results in odd behavior.
+		// To prevent that, pretend the skill has been active for a minute (60 seconds)
+		// This will create a lower estimate for the first minute,
+		// but it isn't ridiculous like saying 2 billion XP per hour.
+		long timeElapsedInSeconds = Math.max(60, Duration.between(skillTimeStart, Instant.now()).getSeconds());
 		return (int) ((1.0 / (timeElapsedInSeconds / 3600.0)) * value);
 	}