fix file detection

com.minres.scviewer.database.sqlite/src/com/minres/scviewer/database/sqlite/SQLiteDbLoader.java

@@ -81,6 +81,7 @@ public class SQLiteDbLoader implements IWaveformDbLoader {
 
 	@Override
 	public boolean load(IWaveformDb db, File file) throws Exception {
+		if(file.isDirectory() || !file.exists()) return false;
 		this.db=db;
 		try {
 			FileInputStream fis = new FileInputStream(file);

com.minres.scviewer.database.text/src/com/minres/scviewer/database/text/TextDbLoader.groovy

@@ -64,6 +64,7 @@ public class TextDbLoader implements IWaveformDbLoader{
 
 	@Override
 	boolean load(IWaveformDb db, File file) throws Exception {
+		if(file.isDirectory() || !file.exists()) return false;
 		this.db=db
 		this.streams=[]
 		try {

com.minres.scviewer.database.vcd/src/com/minres/scviewer/database/vcd/VCDDbLoader.java

@@ -79,6 +79,7 @@ public class VCDDbLoader implements IWaveformDbLoader, IVCDDatabaseBuilder {
 	@SuppressWarnings("unchecked")
 	@Override
 	public boolean load(IWaveformDb db, File file) throws Exception {
+		if(file.isDirectory() || !file.exists()) return false;
 		this.db=db;
 		this.maxTime=0;
 		String name = file.getCanonicalFile().getName();

com.minres.scviewer.e4.application/src/com/minres/scviewer/e4/application/parts/WaveformViewer.java

@@ -669,7 +669,7 @@ public class WaveformViewer implements IFileChangeListener, IPreferenceChangeLis
 			}
 			if (filesToLoad.size() > 0)
 				loadDatabase(persistedState);
-			if(partConfig instanceof String) {
+			if(partConfig instanceof String && ((String)partConfig).length()>0) {
 				loadState((String) partConfig);
 			}
 		}