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Error while iteration on map values after removal

Hi,
I experienced strange behaviour of OHMap after removal of element. Here is sample code to generate issue:

    String KEY = "KEY";
    String VALUE = "VALUE";
    OHMap<String, String> ohMap = new OHMap<>(10);
    ohMap.put(KEY, VALUE);
    ohMap.remove(KEY);
    Iterator<String> iterator = ohMap.values().iterator();
    if (iterator.hasNext()) {
        iterator.next();
    }

It generates JVM crash:

# 
# A fatal error has been detected by the Java Runtime Environment:
#
#  SIGSEGV (0xb) at pc=0x00007f2a1f9c9aed, pid=25433, tid=0x00007f2a1e608700
#
# JRE version: OpenJDK Runtime Environment (8.0_242-b08) (build 1.8.0_242-8u242-b08-0ubuntu3~18.04-b08)
# Java VM: OpenJDK 64-Bit Server VM (25.242-b08 mixed mode linux-amd64 compressed oops)
# Problematic frame:
# V  [libjvm.so+0xa81aed]

or Exception:

java.lang.NegativeArraySizeException
	at com.cfelde.bohmap.BOHMap$ValuesIterator.next(BOHMap.java:1009)
	at com.cfelde.bohmap.BOHMap$ValuesIterator.next(BOHMap.java:944)
	at com.cfelde.bohmap.OHMap$Values$1.next(OHMap.java:282)
	at com.cfelde.bohmap.OHMap$Values$1.next(OHMap.java:274)

It looks like iterator#hasNext return true, but Iterator#next causes exception/crash.

BOHMap can crash JVM

BOHMap calculates offset into the partition using the following code:

 final int hash = Math.abs(hashFunction.apply(keyData));
 final long offset = hash % partitionCount;

If hashFunction returns Integer.MIN_VALUE (i.e. -2147483648) Math.abs will return a negative number. A native offset into a buffer most of the time will crash the process, if not worse.

Check out, for example, this explanation.

This can be easily fixed by doing something like this instead:

final long offset = Math.abs(hashFunction.apply(keyData) % partitionCount);

I actually have a proper fix. Should I open a PR?

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