SortedNodeStore::publishGroup: out of bounds read

Fixes the issued identified by @freeExec in #661

This code is a bit gross. It intentionally loops 1 past the size of the
vector to ensure that we "publish" all the chunks.

There's a similar loop at lines 511-602.

In both loops, there's sort of three chunks of code, which I'll
call "pre", "body" and "post". The pre/post sections need to be guarded,
and the guard for the first loop's "post" section was missing.

Looking at it with fresh eyes, I think we could extract the "body" parts
of both loops to their own functions, and then just call them again
after the loop ends. For now, I'm inclined to let a sleeping dog lie,
but if more work happens in here, that'd be a good cleanup step.

This was also visible in valgrind, as it turns out--the error
goes away with this change:

```
==1968107== Invalid read of size 4
==1968107==    at 0x33ABCD: SortedNodeStore::publishGroup(std::vector<std::pair<unsigned long, LatpLon>, std::allocator<std::pair<unsigned long, LatpLon> > > const&) (in /usr/local/bin/tilemaker)
==1968107==    by 0x33B715: SortedNodeStore::finalize(unsigned long) (in /usr/local/bin/tilemaker)
==1968107==    by 0x2FEE77: PbfProcessor::ReadPbfFile(unsigned int, bool, SignificantTags const&, SignificantTags const&, unsigned int, std::function<std::shared_ptr<std::istream> ()> const&, std::function<std::shared_ptr<OsmLuaProcessing> ()> const&, NodeStore const&, WayStore const&) (in /usr/local/bin/tilemaker)
==1968107==    by 0x140801: main (in /usr/local/bin/tilemaker)
```

SortedWayStore has a similar publishGroup function, but its internal
implementation is different and it doesn't have this issue.

src/sorted_node_store.cpp

@@ -423,9 +423,11 @@ void SortedNodeStore::publishGroup(const std::vector<element_t>& nodes) {
 			lastChunk = currentChunk;
 		}
 
-		tmpLatpLons[currentNodeIndex] = nodes[i].second.latp;
-		tmpLatpLons[currentNodeIndex + 256] = nodes[i].second.lon;
-		currentNodeIndex++;
+		if (i != nodes.size()) {
+			tmpLatpLons[currentNodeIndex] = nodes[i].second.latp;
+			tmpLatpLons[currentNodeIndex + 256] = nodes[i].second.lon;
+			currentNodeIndex++;
+		}
 	}
 
 	uint64_t chunks = currentChunkIndex;