Make sure to NUL-terminate the string on end-of-file (and error)

PR: 643

crypto/bio/bf_buff.c

@@ -169,6 +169,7 @@ start:
 			if (i <= 0)
 				{
 				BIO_copy_next_retry(b);
+				*buf='\0';
 				if (i < 0) return((num > 0)?num:i);
 				if (i == 0) return(num);
 				}
@@ -495,6 +496,9 @@ static int buffer_gets(BIO *b, char *buf, int size)
 			if (i <= 0)
 				{
 				BIO_copy_next_retry(b);
+				*buf='\0';
+				fprintf(stderr, "DEBUG[buffer_gets]: i = %d\n",
+					i);
 				if (i < 0) return((num > 0)?num:i);
 				if (i == 0) return(num);
 				}