fix #458, occasional crash in sampleIndividuals()

VERSIONS

@@ -16,6 +16,7 @@ development head (in the master branch):
 	update Robin Hood Hashing to 3.11.5 to get some minor fixes
 	update zlib from 1.2.13 to 1.3.1 to get some minor fixes
 	some fixes under the hood to make filesystem paths on Windows, using \ instead of /, be better understood by Eidos
+	fix an occasional crash in sampleIndividuals() due to an off-by-one error in buffer sizing
 
 
 version 4.2.2 (Eidos version 3.2.2):

core/subpopulation.cpp

@@ -7734,9 +7734,9 @@ EidosValue_SP Subpopulation::ExecuteMethod_sampleIndividuals(EidosGlobalStringID
 		static int *index_buffer = nullptr;
 		static int buffer_capacity = 0;
 
-		if (last_candidate_index > buffer_capacity)		// just make it big enough for last_candidate_index, not worth worrying
+		if (last_candidate_index + 1 > buffer_capacity)		// just make it big enough for last_candidate_index, not worth worrying
 		{
-			buffer_capacity = last_candidate_index * 2;		// double whenever we go over capacity, to avoid reallocations
+			buffer_capacity = (last_candidate_index + 1) * 2;		// double whenever we go over capacity, to avoid reallocations
 			if (index_buffer)
 				free(index_buffer);
 			index_buffer = (int *)malloc(buffer_capacity * sizeof(int));	// no need to realloc, we don't need the old data