fix some static analyzer reports (Null pointer Dereferences)

src/mtp_properties.c

@@ -675,6 +675,19 @@ int build_DevicePropValue_dataset(mtp_ctx * ctx,void * buffer, int maxsize,uint3
 int objectproplist_element(mtp_ctx * ctx, void * buffer, int * ofs, int maxsize, uint16_t prop_code, uint32_t handle, void * data,uint32_t prop_code_param)
 {
 	int i;
+	uint64_t tmp_data[2];
+	void * tmp_ptr;
+
+	if( !ofs )
+		return 0;
+
+	tmp_data[0] = 0;
+	tmp_data[1] = 0;
+
+	if( data )
+		tmp_ptr = data;
+	else
+		tmp_ptr = (void*)&tmp_data;
 
 	if( (prop_code != prop_code_param) && (prop_code_param != 0xFFFFFFFF) )
 	{
@@ -695,28 +708,25 @@ int objectproplist_element(mtp_ctx * ctx, void * buffer, int * ofs, int maxsize,
 		switch(properties[i].data_type)
 		{
 			case MTP_TYPE_STR:
-				if(data)
-					*ofs = poke_string(buffer, *ofs, maxsize, (char*)data);
-				else
-					*ofs = poke08(buffer, *ofs, maxsize, 0);
+				*ofs = poke_string(buffer, *ofs, maxsize, (char*)tmp_ptr);
 			break;
 			case MTP_TYPE_UINT8:
-				*ofs = poke08(buffer, *ofs, maxsize, *((uint8_t*)data));
+				*ofs = poke08(buffer, *ofs, maxsize, *((uint8_t*)tmp_ptr));
 			break;
 			case MTP_TYPE_UINT16:
-				*ofs = poke16(buffer, *ofs, maxsize, *((uint16_t*)data));
+				*ofs = poke16(buffer, *ofs, maxsize, *((uint16_t*)tmp_ptr));
 			break;
 			case MTP_TYPE_UINT32:
-				*ofs = poke32(buffer, *ofs, maxsize, *((uint32_t*)data));
+				*ofs = poke32(buffer, *ofs, maxsize, *((uint32_t*)tmp_ptr));
 			break;
 			case MTP_TYPE_UINT64:
-				*ofs = poke32(buffer, *ofs, maxsize, *((uint64_t*)data) & 0xFFFFFFFF);
-				*ofs = poke32(buffer, *ofs, maxsize, *((uint64_t*)data) >> 32);
+				*ofs = poke32(buffer, *ofs, maxsize, *((uint64_t*)tmp_ptr) & 0xFFFFFFFF);
+				*ofs = poke32(buffer, *ofs, maxsize, *((uint64_t*)tmp_ptr) >> 32);
 			break;
 			case MTP_TYPE_UINT128:
 				for(i=0;i<4;i++)
 				{
-					*ofs = poke32(buffer, *ofs, maxsize, *((uint32_t*)data)+i);
+					*ofs = poke32(buffer, *ofs, maxsize, *((uint32_t*)tmp_ptr)+i);
 				}
 			break;
 			default: