Avoid crash when glGetString(GL_EXTENSIONS) returns nullptr.

src/Context.cpp

@@ -213,7 +213,10 @@ Context::Context() {
 
     /* OpenGL 2.1 / OpenGL ES 2.0 doesn't have glGetStringi() */
     } else {
-        vector<string> extensions = Corrade::Utility::split(reinterpret_cast<const char*>(glGetString(GL_EXTENSIONS)), ' ');
+        /* Don't crash when glGetString() returns nullptr */
+        const char* e = reinterpret_cast<const char*>(glGetString(GL_EXTENSIONS));
+        if(e) {
+            vector<string> extensions = Corrade::Utility::split(e, ' ');
             for(const string& extension: extensions) {
                 auto found = futureExtensions.find(extension);
                 if(found != futureExtensions.end()) {
@@ -222,6 +225,7 @@ Context::Context() {
                 }
             }
         }
+    }
 
     /* Set this context as current */
     CORRADE_ASSERT(!_current, "Context: Another context currently active", );