Fix process not starting if output directory didn't exist

The error was silently swallowed by the JavaFX thread handler.
It is not properly captured, but more importantly before saving
the config file we make sure the output directory is created.

jsolex-core/src/main/java/me/champeau/a4j/jsolex/processing/params/ProcessParamsIO.java

@@ -17,6 +17,8 @@
 
 import com.google.gson.Gson;
 import me.champeau.a4j.ser.ColorMode;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import java.io.File;
 import java.io.FileInputStream;
@@ -33,6 +35,8 @@
 import java.time.ZonedDateTime;
 
 abstract class ProcessParamsIO {
+    private static final Logger LOGGER = LoggerFactory.getLogger(ProcessParamsIO.class);
+
     private ProcessParamsIO() {
 
     }
@@ -61,6 +65,7 @@ public static ProcessParams loadDefaults() {
         if (params != null) {
             return params;
         }
+        LOGGER.info("No config file found at {}. Using default parameters", defaultsFile);
         return new ProcessParams(
                 new SpectrumParams(SpectralRay.H_ALPHA, SpectralRay.H_ALPHA.getDetectionThreshold(), 0, 3),
                 new ObservationDetails(
@@ -134,9 +139,12 @@ public static ProcessParams readFrom(Path configFile) {
     }
 
     public static void saveTo(ProcessParams params, File destination) {
-        try (var writer = new OutputStreamWriter(new FileOutputStream(destination), StandardCharsets.UTF_8)) {
-            var gson = newGson();
-            writer.write(gson.toJson(params));
+        try {
+            Files.createDirectories(destination.getParentFile().toPath());
+            try (var writer = new OutputStreamWriter(new FileOutputStream(destination), StandardCharsets.UTF_8)) {
+                var gson = newGson();
+                writer.write(gson.toJson(params));
+            }
         } catch (Exception e) {
             throw new RuntimeException(e);
         }