Megamap: the zoom button zooms on the hero and follows him

The zoom button never set the zoom point, so it zoomed on the last
magnifier point (or 0,0). While the button's zoom is on, the point is put on
the hero's map pixel every engine tick; the held mouse button still zooms on
the mouse. game::UiWindow / UiWindowShown shared from windows.h.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

tools/names.txt

@@ -404,3 +404,7 @@
 0x00622e30 Sector_Region                      # thiscall: region number (sector +0x17c -> +0xd7)
 0x00425370 Region_NameKey                     # cdecl (char region): name text key from the region name table 0xaa8ca8, or null
 0x00425300 Region_GetInfo                     # cdecl (char region, out, out): table +0x38 / +0x30 of the region's record
+0x006cb130 cUI_Megamap::WorldToMapPixel        # thiscall (out vec3, world vec3 x/y/level), ret 8: x * 0.007446 + 1018.75, y * 0.014914 - 186.95 (after 0x622700)
+0x0054fa30 cCreature::IsQuestNpc               # thiscall, plain ret: +0x200 bit 0x100 / 0x200, or dialog +0x245 of a type < 50; white on the zoomed map view
+0x00549790 cCreature::GetDialog                # thiscall: dialog +0x245, or a random NPC chatter text (returns 0xd431)
+0x0049a180 cDialogManager::DialogType         # thiscall (dialog, creature), ret 8: record +0x48 of 0x50-byte records at +0x755c; creature flags 0x1000.. -> 0x20..0x23