Fixed crash when RunInSeriesFP's color input is nil

src/gpu/GrFragmentProcessor.cpp

Index: src/gpu/GrFragmentProcessor.cpp
diff --git a/src/gpu/GrFragmentProcessor.cpp b/src/gpu/GrFragmentProcessor.cpp
index 96a0f716c93749f4b7a7698d10f05be84c47f357..bad7ebe0360cd046262d39b4fa639aeecb874445 100644
--- a/src/gpu/GrFragmentProcessor.cpp
+++ b/src/gpu/GrFragmentProcessor.cpp
@@ -310,9 +310,11 @@ sk_sp<GrFragmentProcessor> GrFragmentProcessor::RunInSeries(sk_sp<GrFragmentProc
             class GLFP : public GrGLSLFragmentProcessor {
             public:
                 void emitCode(EmitArgs& args) override {
-                    SkString input(args.fInputColor);
-                    for (int i = 0; i < this->numChildProcessors() - 1; ++i) {
-                        SkString temp;
+                    // First guy's input might be nil.
+                    SkString temp("out0");
+                    this->emitChild(0, args.fInputColor, &temp, args);
+                    SkString input = temp;
+                    for (int i = 1; i < this->numChildProcessors() - 1; ++i) {
                         temp.printf("out%d", i);
                         this->emitChild(i, input.c_str(), &temp, args);
                         input = temp;