pdfviewer: fix bug, page -1 means render page 0 with no page extension

experimental/PdfViewer/pdf_viewer_main.cpp

 #include "SkCanvas.h"
 #include "SkDevice.h"
 #include "SkForceLinking.h"
 #include "SkGraphics.h"
 #include "SkImageDecoder.h"
 #include "SkImageEncoder.h"
 #include "SkOSFile.h"
 #include "SkPicture.h"
 #include "SkStream.h"
 #include "SkTypeface.h"
@@ skipping 79 matching lines @@
     bitmap->setConfig(SkBitmap::kARGB_8888_Config, width, height);
 
     bitmap->allocPixels();
     bitmap->eraseColor(color);
 }
 
 /** Write the output of pdf renderer to a file.
  * @param outputDir Output dir.
  * @param inputFilename The skp file that was read.
  * @param renderer The object responsible to write the pdf file.
+ * @param page -1 means there is only one page (0), and render in a file without page extension
  */
 
 static bool render_page(const SkString& outputDir,
                          const SkString& inputFilename,
                          const SkPdfRenderer& renderer,
                          int page) {
     if (outputDir.isEmpty()) {
         SkBitmap bitmap;
         setup_bitmap(&bitmap, 1, 1);
         SkAutoTUnref<SkDevice> device(SkNEW_ARGS(SkDevice, (bitmap)));
@@ skipping 13 matching lines @@
     setup_bitmap(&bitmap, 3 * (int)SkScalarToDouble(rect.width()), 3 * (int)SkScalarToDouble(rect.height()));
 #else
     setup_bitmap(&bitmap, (int)SkScalarToDouble(rect.width()), (int)SkScalarToDouble(rect.height()));
 #endif
     SkAutoTUnref<SkDevice> device(SkNEW_ARGS(SkDevice, (bitmap)));
     SkCanvas canvas(device);
 
     gDumpBitmap = &bitmap;
 
     gDumpCanvas = &canvas;
-    renderer.renderPage(page, &canvas);
+    renderer.renderPage(page < 0 ? 0 : page, &canvas);
 
     SkImageEncoder::EncodeFile(outputPath.c_str(), bitmap, SkImageEncoder::kPNG_Type, 100);
 
     return true;
 }
 
 /** Reads an skp file, renders it to pdf and writes the output to a pdf file
  * @param inputPath The skp file to be read.
  * @param outputDir Output dir.
  * @param renderer The object responsible to render the skp object into pdf.
@@ skipping 115 matching lines @@
     }
 
     return 0;
 }
 
 #if !defined SK_BUILD_FOR_IOS
 int main(int argc, char * const argv[]) {
     return tool_main(argc, (char**) argv);
 }
 #endif