PLT-6057: Fix empty search results with in/from. (#5892)

When search query was empty but in/from was set, search results didn't
include posts containing hashtags.

model/search_params.go

@@ -165,7 +165,7 @@ func ParseSearchParams(text string) []*SearchParams {
 	if len(plainTerms) == 0 && len(hashtagTerms) == 0 && (len(inChannels) != 0 || len(fromUsers) != 0) {
 		paramsList = append(paramsList, &SearchParams{
 			Terms:      "",
-			IsHashtag:  true,
+			IsHashtag:  false,
 			InChannels: inChannels,
 			FromUsers:  fromUsers,
 		})