fix: return negative on error

src/triangle.cpp

@@ -57,7 +57,7 @@ GLint Triangle::getShaderUniformLocation(const std::string& uniformName)
     if (location == -1)
     {
         std::cerr << "Could not find uniform: " << uniformName << std::endl;
-        return 0;
+        return -1;
     }
 
     return location;