Fixes the following GCC warning:
````
drape_frontend/circles_pack_shape.cpp:133:9: warning: ‘void* memset(void*, int, size_t)’
clearing an object of non-trivial type ‘struct df::CirclesPackDynamicVertex’;
use assignment or value-initialization instead [-Wclass-memaccess]
133 | memset(m_buffer.data(), 0, m_buffer.size() * sizeof(CirclesPackDynamicVertex));
| ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
````
Signed-off-by: Ferenc Géczi <ferenc.gm@gmail.com>
