Absurd texture name in error message

When a map has a missing flat or texture, the game aborts with an error message, either R_FlatNumForName: %s not found or R_TextureNumForName: %s not found.

Sidedefs pack the upper, middle, and lower texture names (in that order) in arrays of eight characters, without using a separator. Sectors pack floor and ceiling flat names in a similar way. When a texture or flat is missing, the error string is printed using the corresponding array to be inserted as the %s token. Since C uses s, if the texture or flat name is full (it uses all eight characters available) then the formatting function will keep adding the next characters in memory until it finds a null.

For example, if a sidedef is given a non-existent upper texture with a name using all eight characters, then the name of the next texture in order (middle texture) will be appended (regardless of whether it is missing or not). If that one is also full, the lower texture name will be appended too. And if the lower texture name is full, garbage characters will be added as the sidedef's sector number is processed, followed by the offsets, texture names, and sector number of the next sidedef, and so on, until a null byte is finally encountered, preferably before a happens.