Bug 1639033 - Fix signed-unsigned comparison warning in basicutil.c. …

…r=kjacobs

Differential Revision: https://phabricator.services.mozilla.com/D75840

--HG--
extra : moz-landing-system : lando

cmd/lib/basicutil.c

@@ -17,6 +17,7 @@
 
 #include "basicutil.h"
 #include <stdarg.h>
+#include <stddef.h>
 #include <sys/stat.h>
 #include <errno.h>
 
@@ -632,7 +633,8 @@ void
 SECU_PrintPRandOSError(const char *progName)
 {
     char buffer[513];
-    PRInt32 errLen = PR_GetErrorTextLength();
+    PRInt32 errLenInt = PR_GetErrorTextLength();
+    size_t errLen = errLenInt < 0 ? 0 : (size_t)errLenInt;
     if (errLen > 0 && errLen < sizeof buffer) {
         PR_GetErrorText(buffer);
     }