Let return dummy TGPicture in batch mode

In batch real pixmap manipulation is not possible.
But all instances of TGPicture are created.
In normal mode they are "hidden", but in batch one can return pointer on the picture to suppress many
errors printout in the TG.. classes

By the way - by the first call of `TGPicturePool::GetPicture()` also dummy ` TGPicture` is returned

Author: linev

gui/gui/src/TGPicture.cxx

@@ -94,42 +94,36 @@ const TGPicture *TGPicturePool::GetPicture(const char *name)
 
    TGPicture *pic = (TGPicture *)fPicList->FindObject(pname);
    if (pic && !pic->IsScaled()) {
-      if (pic->fPic == kNone)
-         return 0;
+      // in batch mode allow to return dummy image
+      if ((pic->fPic == kNone) && !gROOT->IsBatch())
+         return nullptr;
       pic->AddReference();
       return pic;
    }
 
    char *picnam = gSystem->Which(fPath, pname, kReadPermission);
-   if (!picnam) {
-      pic = new TGPicture(pname);
-      pic->fAttributes.fColormap  = fClient->GetDefaultColormap();
-      pic->fAttributes.fCloseness = 40000; // Allow for "similar" colors
-      pic->fAttributes.fMask      = kPASize | kPAColormap | kPACloseness;
-      fPicList->Add(pic);
-      return 0;
-   }
 
-   TImage *img = TImage::Open(picnam);
+   TImage *img = picnam ? TImage::Open(picnam) : nullptr;
+
+   delete [] picnam;
+
    if (!img) {
       pic = new TGPicture(pname);
       pic->fAttributes.fColormap  = fClient->GetDefaultColormap();
       pic->fAttributes.fCloseness = 40000; // Allow for "similar" colors
       pic->fAttributes.fMask      = kPASize | kPAColormap | kPACloseness;
       fPicList->Add(pic);
-      delete [] picnam;
-      return 0;
+      return nullptr;
    }
 
    pic = new TGPicture(pname, img->GetPixmap(), img->GetMask());
-   delete [] picnam;
    delete img;
    fPicList->Add(pic);
    return pic;
 }
 
 ////////////////////////////////////////////////////////////////////////////////
-/// Like TGPicturePool::GetPicture() but, instead of returning null when the 
+/// Like TGPicturePool::GetPicture() but, instead of returning null when the
 /// picture is not found, it returns a valid empty picture.
 
 const TGPicture *TGPicturePool::GetPictureOrEmpty(const char *name)