Optional width and height parameters for thumbnailer

This is to generate custom sized images from SVGs, defaults will still work the same as before.

Diffs=
434223338 Optional width and height parameters for thumbnailer

.rive_head

diff --git a/.rive_head b/.rive_head
index f2f0e15..b77e8cb 100644
--- a/.rive_head
+++ b/.rive_head
@@ -1 +1 @@
-a1d921c85a7c4057dbebf972939e188a3d515c86
+4342233383156cba2154ad05b74157b139dc8bfc

skia/thumbnail_generator/src/main.cpp

diff --git a/skia/thumbnail_generator/src/main.cpp b/skia/thumbnail_generator/src/main.cpp
index cfc4eb5..f804338 100644
--- a/skia/thumbnail_generator/src/main.cpp
+++ b/skia/thumbnail_generator/src/main.cpp
@@ -9,6 +9,8 @@
 #include <cstdio>
 #include <stdio.h>
 #include <string>
+#include <iostream>
+#include <sstream>
 
 std::string getFileName(char* path) {
     std::string str(path);
@@ -18,6 +20,19 @@
     return str.substr(from + 1, to - from - 1);
 }
 
+const int DEFAULT_SIZE = 256;
+
+int getArg(char* arg) {
+    std::istringstream ss(arg);
+    int x;
+    if (!(ss >> x)) {
+        std::cerr << "Invalid number: " << arg << '\n';
+    } else if (!ss.eof()) {
+        std::cerr << "Trailing chars after number: " << arg << '\n';
+    }
+    return x == 0 ? DEFAULT_SIZE : x;
+}
+
 int main(int argc, char* argv[]) {
     rive::SkiaFactory factory;
 
@@ -38,6 +53,12 @@
         outPath = fullName.c_str();
     }
 
+    int width = DEFAULT_SIZE, height = DEFAULT_SIZE;
+    if (argc == 5) {
+        width = getArg(argv[3]);
+        height = getArg(argv[4]);
+    }
+
     if (fp == nullptr) {
         fprintf(stderr, "Failed to open rive file.\n");
         return 1;
@@ -61,8 +82,6 @@
     auto artboard = file->artboardDefault();
     artboard->advance(0.0f);
 
-    int width = 256, height = 256;
-
     sk_sp<SkSurface> rasterSurface = SkSurface::MakeRasterN32Premul(width, height);
     SkCanvas* rasterCanvas = rasterSurface->getCanvas();