runtime_loader: Fix endless rld heap grow loop in edge case.

The needed storage space for tracking the allocation size was not
accounted for when growing the heap. Since the growth size is always
rounded up to a multiple of 32KiB, this did almost never matter as the
new allocation wouldn't need the full size. If the allocation did
happen to need the full size however, the newly added area would always
be too small. As the allocation attempt was simply restarted after each
successful growth, this lead to an endless loop creating small new
areas, which would then quickly starve the system for memory.

src/system/runtime_loader/heap.cpp

@@ -202,7 +202,7 @@ grow_heap(size_t bytes)
 {
 	// align the area size to an 32768 bytes boundary
 	bytes = (bytes + 32767) & ~32767;
-	return add_area(bytes);
+	return add_area(bytes + sizeof(size_t));
 }