logfmt: don't omit last item if it does not have a value

A line like `foo=bar baz` should be parsed to `{"foo"=>"bar", "baz"=>nil}`, but `baz` was silently omitted by returning early from the parser.

src/flb_parser_logfmt.c

@@ -99,17 +99,14 @@ static int logfmt_parser(struct flb_parser *parser,
         while ((c < end) && ident_byte[*c]) {
             c++;
         }
-        if (c == end) {
-            break;
-        }
 
         key_len = c - key;
         /* value */
         value_len = 0;
         value_str = FLB_FALSE;
         value_escape =  FLB_FALSE;
 
-        if (*c == '=') {
+        if (c < end && *c == '=') {
             c++;
             if (c < end) {
                 if (*c == '"') {