Do not complain on NULL returned when allocating 0 objects

According to documentation on malloc/calloc, when zero allocation size
is requested, it is allowed to return either unique pointer or NULL.
In the latter case, FMU was previously incorrectly complaining about
"out of memory".

Belonging to [master]:
  - OpenModelica/OMCompiler#2844

SimulationRuntime/c/simulation/solver/model_help.c

@@ -894,14 +894,14 @@ void initializeDataStruc(DATA *data, threadData_t *threadData)
     tmpSimData.timeValue = 0;
     /* buffer for all variable values */
     tmpSimData.realVars = (modelica_real*) calloc(data->modelData->nVariablesReal, sizeof(modelica_real));
-    assertStreamPrint(threadData, 0 != tmpSimData.realVars, "out of memory");
+    assertStreamPrint(threadData, 0 == data->modelData->nVariablesReal || 0 != tmpSimData.realVars, "out of memory");
     tmpSimData.integerVars = (modelica_integer*) calloc(data->modelData->nVariablesInteger, sizeof(modelica_integer));
-    assertStreamPrint(threadData, 0 != tmpSimData.integerVars, "out of memory");
+    assertStreamPrint(threadData, 0 == data->modelData->nVariablesInteger || 0 != tmpSimData.integerVars, "out of memory");
     tmpSimData.booleanVars = (modelica_boolean*) calloc(data->modelData->nVariablesBoolean, sizeof(modelica_boolean));
-    assertStreamPrint(threadData, 0 != tmpSimData.booleanVars, "out of memory");
+    assertStreamPrint(threadData, 0 == data->modelData->nVariablesBoolean || 0 != tmpSimData.booleanVars, "out of memory");
 #if !defined(OMC_NVAR_STRING) || OMC_NVAR_STRING>0
     tmpSimData.stringVars = (modelica_string*) omc_alloc_interface.malloc_uncollectable(data->modelData->nVariablesString * sizeof(modelica_string));
-    assertStreamPrint(threadData, 0 != tmpSimData.stringVars, "out of memory");
+    assertStreamPrint(threadData, 0 == data->modelData->nVariablesString || 0 != tmpSimData.stringVars, "out of memory");
 #endif
     appendRingData(data->simulationData, &tmpSimData);
   }
@@ -1045,7 +1045,7 @@ void initializeDataStruc(DATA *data, threadData_t *threadData)
   data->simulationInfo->extObjs = NULL;
   data->simulationInfo->extObjs = (void**) calloc(data->modelData->nExtObjs, sizeof(void*));
 
-  assertStreamPrint(threadData, 0 != data->simulationInfo->extObjs, "error allocating external objects");
+  assertStreamPrint(threadData, 0 == data->modelData->nExtObjs || 0 != data->simulationInfo->extObjs, "error allocating external objects");
 
 #if !defined(OMC_MINIMAL_LOGGING)
   /* initial chattering info */
@@ -1083,7 +1083,7 @@ void initializeDataStruc(DATA *data, threadData_t *threadData)
   /* initial delay */
 #if !defined(OMC_NDELAY_EXPRESSIONS) || OMC_NDELAY_EXPRESSIONS>0
   data->simulationInfo->delayStructure = (RINGBUFFER**)malloc(data->modelData->nDelayExpressions * sizeof(RINGBUFFER*));
-  assertStreamPrint(threadData, 0 != data->simulationInfo->delayStructure, "out of memory");
+  assertStreamPrint(threadData, 0 == data->modelData->nDelayExpressions || 0 != data->simulationInfo->delayStructure, "out of memory");
 
   for(i=0; i<data->modelData->nDelayExpressions; i++)
     data->simulationInfo->delayStructure[i] = allocRingBuffer(1024, sizeof(TIME_AND_VALUE));