Fix an issue with the IPP backend and unsupported "sides" values (rdar://51775322)

.gitattributes

@@ -1,3 +1,5 @@
 .git* export-ignore
 .mailmap export-ignore
+examples/testfile.pcl -text
+exampels/testfile.txt -text
 scripts export-ignore

CHANGES.md

@@ -11,6 +11,8 @@ Changes in CUPS v2.3.0
 - Removed dead code from the scheduler (Issue #5593)
 - "make" failed with GZIP options (Issue #5595)
 - Fixed a NULL pointer dereference bug in `httpGetSubField2` (Issue #5598)
+- Fixed an issue with unsupported "sides" values in the IPP backend
+  (rdar://51775322)
 - Fixed an issue with `EXPECT !name WITH-VALUE ...` tests.
 - Fixed a command ordering issue in the Zebra ZPL driver.
 

backend/ipp.c

@@ -1504,7 +1504,7 @@ main(int  argc,				/* I - Number of command-line args */
 
         const char *sides = cupsGetOption("sides", num_options, options);
 
-        if (!strncmp(sides, "two-sided-", 10))
+        if (!sides || !strncmp(sides, "two-sided-", 10))
         {
           fputs("DEBUG: Unable to do two-sided printing, setting sides to 'one-sided'.\n", stderr);
           num_options = cupsAddOption("sides", "one-sided", num_options, &options);