Disable buffer completion when there is no prefix/suffix

We still enable it when a custom completion command provides us with completion candidates. For example user might hit escape in a context where a file name should be inserted, without providing any initial prefix or suffix (as the number of expected candidates is small).

Frameworks/editor/src/completion.cc

@@ -113,6 +113,9 @@ namespace ng
 			}
 		}
 
+		if(commandResult.empty() && prefix.empty() && suffix.empty())
+			return { };
+
 		for(ssize_t i = 0; i < commandResult.size(); ++i)
 			tmp.push_back(std::make_pair(-commandResult.size() + i, commandResult[i]));