Fix another segfault in 1998/schnitzi

The program would also crash if the arg had any character that's not a
digit or if the arg had only 0s in it (it would work if it had 0
followed by a digit other than 0). In other words if it is converted to
0 it would segfault.

The bugs.md file has been updated as well to note what's also now in the
README.md file: even a relatively small number can cause a substantial
amount of lines of output. For instance the number 9 causes 771999 lines
(!!) of output.

bugs.md

@@ -93,7 +93,8 @@ formatting code.
 ## STATUS: INABIAF - please **DO NOT** fix
 ### INABIAF: It's not a bug it's a feature :-)
 
-Entries with this status should NOT be touched: they are system specific by design
+Entries with this status should NOT be touched (unless they have another status
+that suggests that issue can be changed): they are system specific by design
 or are other things that are not actually bugs even if they appear to be but are
 noteworthy nonetheless.
 
@@ -516,6 +517,15 @@ Please DO NOT change this either.
 If there are any other warnings triggered by your compiler please DO NOT fix
 those either!
 
+Another important note is that as the number passed into the program gets bigger
+the number of lines of output gets substantially larger. For instance:
+
+```sh
+$ ./schnitzi 9|wc -l
+  771999
+```
+
+
 # 1999
 
 There was no IOCCC in 1999.