LibELF: Fix 'applying offset produced null pointer' UBSAN failure

These integer => pointer => integer conversions were technically prone
to UB, since they were used as offsets (which are perfectly fine to be
zero), but we calculated them with pointer arithmetic. This made Clang
insert pointer overflow UBSAN checks, which trigger in case of a zero
result.

Userland/Libraries/LibELF/DynamicLoader.cpp

@@ -321,7 +321,7 @@ void DynamicLoader::load_program_headers()
     for (auto& text_region : text_regions) {
         FlatPtr ph_text_desired_base = text_region.desired_load_address().get();
         FlatPtr ph_text_base = text_region.desired_load_address().page_base().get();
-        FlatPtr ph_text_end = ph_text_base + round_up_to_power_of_two(text_region.size_in_memory() + (size_t)(text_region.desired_load_address().as_ptr() - ph_text_base), PAGE_SIZE);
+        FlatPtr ph_text_end = ph_text_base + round_up_to_power_of_two(text_region.size_in_memory() + text_region.desired_load_address().get() - ph_text_base, PAGE_SIZE);
 
         // Now we can map the text segment at the reserved address.
         auto* text_segment_begin = (u8*)mmap_with_name(
@@ -355,7 +355,7 @@ void DynamicLoader::load_program_headers()
 
     for (auto& data_region : data_regions) {
         FlatPtr ph_data_base = data_region.desired_load_address().page_base().get();
-        FlatPtr ph_data_end = ph_data_base + round_up_to_power_of_two(data_region.size_in_memory() + (size_t)(data_region.desired_load_address().as_ptr() - ph_data_base), PAGE_SIZE);
+        FlatPtr ph_data_end = ph_data_base + round_up_to_power_of_two(data_region.size_in_memory() + data_region.desired_load_address().get() - ph_data_base, PAGE_SIZE);
 
         auto* data_segment_address = (u8*)reservation + ph_data_base - ph_load_base;
         size_t data_segment_size = ph_data_end - ph_data_base;