cairo-trace: Fix escape character encoding in string literals

This fixes a typo wherein both a return character and a tab character were encoded when only a return character was specified for encoding.

The corresponding CairoScript-interpreting code in cairo-script-scanner.c:1143-1145 does not take any special action when encountering a return-specifying sequence followed by a tab-specifiying sequence, leading me to believe that this is a simple typo consisting of a missing break statement. If this is not the case, please let me know and I apologize for the nuisance.

Thank you for taking time to read this.