Avoid ssize_t type, since it is POSIX-specific

Only j could become negative, so we simply check before it would

base58.c

@@ -15,7 +15,6 @@
 #include <stddef.h>
 #include <stdint.h>
 #include <string.h>
-#include <sys/types.h>
 
 #include "libbase58.h"
 
@@ -146,7 +145,7 @@ bool b58enc(char *b58, size_t *b58sz, const void *data, size_t binsz)
 {
 	const uint8_t *bin = data;
 	int carry;
-	ssize_t i, j, high, zcount = 0;
+	size_t i, j, high, zcount = 0;
 	size_t size;
 	
 	while (zcount < binsz && !bin[zcount])
@@ -163,6 +162,10 @@ bool b58enc(char *b58, size_t *b58sz, const void *data, size_t binsz)
 			carry += 256 * buf[j];
 			buf[j] = carry % 58;
 			carry /= 58;
+			if (!j) {
+				// Otherwise j wraps to maxint which is > high
+				break;
+			}
 		}
 	}