Packages: fix -Wstringop-overflow warning

Author: fam007e

src/modules/packages/packages.c

@@ -135,8 +135,8 @@ bool ffPrintPackages(FFPackagesOptions* options) {
         FF_PRINT_PACKAGE(xbps)
 
         assert(output.length >= 2); // counts.all > 0 guarantees that at least one package count was printed, which guarantees that ", " was appended at least once
-        ffStrbufSubstrBefore(&output, output.length - 1);
-        output.chars[output.length - 1] = '\n';
+        ffStrbufSubstrBefore(&output, output.length - 2);
+        ffStrbufAppendC(&output, '\n');
         ffStrbufWriteTo(&output, stdout);
     } else {
         FF_PRINT_FORMAT_CHECKED(FF_PACKAGES_MODULE_NAME,