feat: allow LoRAs with negative multiplier (#83)

* Allow Loras with negative weight, too.

There are a couple of loras, which serve to adjust certain concepts in
both positive and negative directions (like exposure, detail level etc).

The current code rejects them if loaded with a negative weight, but I
suggest that this check can simply be dropped.

* ignore lora in the case of multiplier == 0.f

---------

Co-authored-by: Urs Ganse <urs@nerd2nerd.org>
Co-authored-by: leejet <leejet714@gmail.com>

stable-diffusion.cpp

@@ -276,9 +276,11 @@ std::pair<std::unordered_map<std::string, float>, std::string> extract_and_remov
     while (std::regex_search(text, matches, re)) {
         std::string filename = matches[1].str();
         float multiplier     = std::stof(matches[2].str());
-        if (multiplier < 0.f) {
+
+        if (multiplier == 0.f) {
             continue;
         }
+
         if (filename2multiplier.find(filename) == filename2multiplier.end()) {
             filename2multiplier[filename] = multiplier;
         } else {