global: Avoid loops unnecessarily decreasing below zero.

Avoids complains from clang -fsanitize=integer

src/lib-mail/message-address.c

@@ -337,7 +337,8 @@ static int parse_address_list(struct message_address_parser_context *ctx,
 	int ret = 0;
 
 	/* address-list    = (address *("," address)) / obs-addr-list */
-	while (max_addresses-- > 0) {
+	while (max_addresses > 0) {
+		max_addresses--;
 		if ((ret = parse_address(ctx)) == 0)
 			break;
 		if (*ctx->parser.data != ',') {

src/lib-mail/message-snippet.c

@@ -75,8 +75,9 @@ static bool snippet_generate(struct snippet_context *ctx,
 				if (ctx->chars_left-- == 0)
 					return FALSE;
 			}
-			if (ctx->chars_left-- == 0)
+			if (ctx->chars_left == 0)
 				return FALSE;
+			ctx->chars_left--;
 			count = uni_utf8_char_bytes(data[i]);
 			i_assert(i + count <= size);
 			str_append_n(ctx->snippet, data + i, count);

src/lib/sha3.c

@@ -144,19 +144,23 @@ void sha3_loop(void *context, const void *data, size_t len)
 	if(len < old_tail) { /* have no complete word or haven't started
 			      * the word yet */
 		/* endian-independent code follows: */
-		while (len-- > 0)
+		while (len > 0) {
+			len--;
 			ctx->saved |= (uint64_t) (*(buf++)) <<
 					((ctx->byteIndex++) * 8);
+		}
 		i_assert(ctx->byteIndex < 8);
 		return;
 	}
 
 	if(old_tail != 0) { /* will have one word to process */
 		/* endian-independent code follows: */
 		len -= old_tail;
-		while (old_tail-- > 0)
+		while (old_tail > 0) {
+			old_tail--;
 			ctx->saved |= (uint64_t) (*(buf++)) <<
 				((ctx->byteIndex++) * 8);
+		}
 
 		/* now ready to add saved to the sponge */
 		ctx->s[ctx->wordIndex] ^= ctx->saved;
@@ -200,7 +204,8 @@ void sha3_loop(void *context, const void *data, size_t len)
 
 	/* finally, save the partial word */
 	i_assert(ctx->byteIndex == 0 && tail < 8);
-	while (tail-- > 0) {
+	while (tail > 0) {
+		tail--;
 		ctx->saved |= (uint64_t) (*(buf++)) << ((ctx->byteIndex++) * 8);
 	}
 	i_assert(ctx->byteIndex < 8);