Audio,GL: shorter way to avoid crashes on nullptr C strings.

This is actually to avoid an ambigous overload with Corrade's new
StringView APIs, but doesn't hurt to commit that anyway.

src/Magnum/Audio/Context.cpp

@@ -333,15 +333,11 @@ std::vector<std::string> Context::extensionStrings() const {
     std::vector<std::string> extensions;
 
     /* Don't crash when alGetString() returns nullptr */
-    const char* alExts = reinterpret_cast<const char*>(alGetString(AL_EXTENSIONS));
-    if(alExts) extensions = Utility::String::splitWithoutEmptyParts(alExts, ' ');
+    extensions = Utility::String::splitWithoutEmptyParts(Utility::String::fromArray(reinterpret_cast<const char*>(alGetString(AL_EXTENSIONS))), ' ');
 
     /* Add ALC extensions as well */
-    const char* alcExts = reinterpret_cast<const char*>(alcGetString(_device, ALC_EXTENSIONS));
-    if(alcExts) {
-        auto splitAlcExts = Utility::String::splitWithoutEmptyParts(alcExts, ' ');
+    auto splitAlcExts = Utility::String::splitWithoutEmptyParts(Utility::String::fromArray(reinterpret_cast<const char*>(alcGetString(_device, ALC_EXTENSIONS))), ' ');
     extensions.insert(extensions.end(), splitAlcExts.begin(), splitAlcExts.end());
-    }
 
     return extensions;
 }

src/Magnum/GL/Context.cpp

@@ -985,8 +985,7 @@ std::vector<std::string> Context::extensionStrings() const {
     {
         /* Don't crash when glGetString() returns nullptr (i.e. don't trust the
            old implementations) */
-        const char* e = reinterpret_cast<const char*>(glGetString(GL_EXTENSIONS));
-        if(e) extensions = Utility::String::splitWithoutEmptyParts(e, ' ');
+        extensions = Utility::String::splitWithoutEmptyParts(Utility::String::fromArray(reinterpret_cast<const char*>(glGetString(GL_EXTENSIONS))), ' ');
     }
     #endif