Regression: ensure native library is loaded in static methods as needed.

Regression from:
c9ff41f In-memory: use native implementation for deleteAllFiles #194

Notably when calling the static deleteAllFiles which now uses a native
implementation.

Author: greenrobot-team

objectbox-java/src/main/java/io/objectbox/BoxStore.java

@@ -453,6 +453,7 @@ public static boolean isDatabaseOpen(File directory) throws IOException {
      */
     @Experimental
     public static long sysProcMeminfoKb(String key) {
+        NativeLibraryLoader.ensureLoaded();
         return nativeSysProcMeminfoKb(key);
     }
 
@@ -475,6 +476,7 @@ public static long sysProcMeminfoKb(String key) {
      */
     @Experimental
     public static long sysProcStatusKb(String key) {
+        NativeLibraryLoader.ensureLoaded();
         return nativeSysProcStatusKb(key);
     }
 
@@ -720,6 +722,7 @@ public static boolean deleteAllFiles(File objectStoreDirectory) {
         if (isFileOpen(canonicalPath)) {
             throw new IllegalStateException("Cannot delete files: store is still open");
         }
+        NativeLibraryLoader.ensureLoaded();
         return nativeRemoveDbFiles(canonicalPath, true);
     }