CXX-1476 Fix compare key name error

If a document has a "de" key and a "desc" key, when searching for the "de" key, it may match the "desc" key.
So judge the key length to make sure match the right key.

Author: kevin1018

src/bsoncxx/document/view.cpp

@@ -125,7 +125,7 @@ view::const_iterator view::find(stdx::string_view key) const {
 
     while (bson_iter_next(&iter)) {
         const char* ikey = bson_iter_key(&iter);
-        if (0 == strncmp(key.data(), ikey, key.size())) {
+        if (0 == strncmp(key.data(), ikey, key.size()) && strlen(ikey) == key.size()) {
             return const_iterator(element(iter.raw, iter.len, iter.off));
         }
     }

src/mongocxx/test/collection.cpp

@@ -2336,7 +2336,7 @@ TEST_CASE("create_index tests", "[collection]") {
 
         bool unique = options.unique().value();
         auto validate = [unique](bsoncxx::document::view index) {
-            auto expire_after = index["expireAfter"];
+            auto expire_after = index["expireAfterSeconds"];
             REQUIRE(expire_after);
             REQUIRE(expire_after.type() == type::k_int32);
             REQUIRE(expire_after.get_int32().value == 500);