Replace string constructor with assigment operator (#57)

* avoid null constructor for string constructed from empty
  glGetString(GL_EXTENSIONS)
* bump version v0.3.9

CMakeLists.txt

@@ -14,7 +14,7 @@ HunterGate(
   LOCAL
   )
 
-project(ogles_gpgpu VERSION 0.3.8)
+project(ogles_gpgpu VERSION 0.3.9)
 
 # !!! Make sure option OGLES_GPGPU_OPENG_ES3 occurs prior to the first
 # hunter_add_package() call.  This will allow us to modify settings

ogles_gpgpu/common/core.cpp

@@ -359,8 +359,9 @@ void Core::getOutputData(unsigned char* buf) {
 #pragma mark helper methods
 
 void Core::checkGLExtensions() {
+
     // get string with extensions seperated by a SPACE
-    string glExtString((const char*)glGetString(GL_EXTENSIONS));
+    std::string glExtString = reinterpret_cast<const char *>(glGetString(GL_EXTENSIONS));
 
     // get extensions as vector
     vector<string> glExt = Tools::split(glExtString);