fix broken shgetc limiter logic (wasn't working)

src/internal/shgetc.c

@@ -13,7 +13,10 @@ void __shlim(FILE *f, off_t lim)
 int __shgetc(FILE *f)
 {
 	int c;
-	if (f->shcnt >= f->shlim) return EOF;
+	if (f->shlim && f->shcnt >= f->shlim) {
+		f->shend = 0;
+		return EOF;
+	}
 	c = __uflow(f);
 	if (f->shlim && f->rend - f->rpos > f->shlim - f->shcnt - 1)
 		f->shend = f->rpos + (f->shlim - f->shcnt - 1);

src/internal/shgetc.h

@@ -6,4 +6,4 @@ int __shgetc(FILE *);
 #define shcnt(f) ((f)->shcnt + ((f)->rpos - (f)->rend))
 #define shlim(f, lim) __shlim((f), (lim))
 #define shgetc(f) (((f)->rpos < (f)->shend) ? *(f)->rpos++ : __shgetc(f))
-#define shunget(f) ((f)->rend ? (void)(f)->rpos-- : (void)0)
+#define shunget(f) ((f)->shend ? (void)(f)->rpos-- : (void)0)