refactor(demos): make it easier to distinguish P3 and P6 in error messages

Author: jonasgeiler

demos/lib/ppm.lua

@@ -247,7 +247,7 @@ function ppm.load(path)
 		elseif format == 'P6' then
 			local row_err = read_raw_ppm_row(pixels[row])
 			if row_err then
-				return nil, nil, nil, 'Error reading pixel data: ' .. row_err
+				return nil, nil, nil, 'Error reading raw pixel data: ' .. row_err
 			end
 		end
 	end