Remove segfault from DX11 backend.

Instead of blindly using the expected width, clamp it to the stride of the
buffer which dx11 returns. This prevents use from reading invalid memory
at the end of textures.

This doesn't solve the base issue of what to do when a game tries to copy
from outside the efb. On real hardware it returns random noise (biased
to all ones)

Source/Core/VideoBackends/D3D/PSTextureEncoder.cpp

@@ -152,9 +152,10 @@ void PSTextureEncoder::Encode(u8* dst, const TextureCache::TCacheEntryBase *text
 		CHECK(SUCCEEDED(hr), "map staging buffer (0x%x)", hr);
 
 		u8* src = (u8*)map.pData;
+		u32 readStride = std::min(texture_entry->CacheLinesPerRow() * 32, map.RowPitch);
 		for (unsigned int y = 0; y < texture_entry->NumBlocksY(); ++y)
 		{
-			memcpy(dst, src, texture_entry->CacheLinesPerRow() * 32);
+			memcpy(dst, src, readStride);
 			dst += texture_entry->memory_stride;
 			src += map.RowPitch;
 		}