fix(shorten): exit 3 if removal would leave the file empty

Makefile

@@ -1,5 +1,5 @@
 CC=clang
-CFLAGS=-pedantic -Wall -Wextra -std=c99 -D_GNU_SOURCE -O3
+CFLAGS=-pedantic -Wall -Wextra -std=c99 -D_GNU_SOURCE -Ofast
 
 all: shorten
 

shorten.c

@@ -114,8 +114,8 @@ int main(int argc, char **argv) {
 
     // Beginning of file?
     if (lseek(fd, 0, SEEK_CUR) == 0) {
-      printf("No change: file does not end with a newline\n");
-      return 1;
+      printf("No change: requested removal would leave empty file\n");
+      return 3;
     }
   }