Is that "A full MIP map chain ends with the 1x1 texel texture inclusive" also applied to other texture formats like dxt5 or dxt1?
DXTn is an encoding of texture data. Due to its block nature the last MIP level that fills in the entire block is 4x4 texels. However, with doing some padding one can get down to 1x1 again. Searching for the problem brings e.g. this thread to light, where Evil Steve answers your question in post #5.
Of course, the code snippet in the OP does not consider compression but raw texture data. When considering compression, you should use the mipMaps <= ld( max( width, height ) ) formula instead of the conditional break, and you need to restrict mipHeight and mipWidth to the respective block's edge length instead of 1, and you need to multiply the resulting size with the compression ratio (depending on the compression scheme and sometimes the texel format, but fortunately a fix rate therein).