Adding error messages for negative fuzziness

 Querying for negative fuzziness or edit distance is
 an invalid option and adding error messages for that.
 This would help further wrinkles down the line due to
 wrapping of -ve ED to a higher value during the uint
 typecasting.

search/searcher/search_fuzzy.go

@@ -31,6 +31,10 @@ func NewFuzzySearcher(indexReader index.IndexReader, term string,
 		return nil, fmt.Errorf("fuzziness exceeds max (%d)", MaxFuzziness)
 	}
 
+	if fuzziness < 0 {
+		return nil, fmt.Errorf("invalid fuzziness, negative")
+	}
+
 	// Note: we don't byte slice the term for a prefix because of runes.
 	prefixTerm := ""
 	for i, r := range term {

search/searcher/search_fuzzy_test.go

@@ -140,3 +140,16 @@ func TestFuzzySearch(t *testing.T) {
 		}
 	}
 }
+
+func TestFuzzySearchLimitErrors(t *testing.T) {
+	explainTrue := search.SearcherOptions{Explain: true}
+	_, err := NewFuzzySearcher(nil, "water", 3, 3, "desc", 1.0, explainTrue)
+	if err == nil {
+		t.Fatal("`fuzziness exceeds max (2)` error expected")
+	}
+
+	_, err = NewFuzzySearcher(nil, "water", 3, -1, "desc", 1.0, explainTrue)
+	if err == nil {
+		t.Fatal("`invalid fuzziness, negative` error expected")
+	}
+}