Move setSampleMatrix and setSampledWithExplicitCoords into child registration

Bug: skia:10396
Change-Id: I0c117ab4d95737b76dec5bce16103b9058218fb8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/297065
Commit-Queue: Michael Ludwig <michaelludwig@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
diff --git a/src/gpu/glsl/GrGLSLGeometryProcessor.cpp b/src/gpu/glsl/GrGLSLGeometryProcessor.cpp
index 334b35b..4d2ee7e 100644
--- a/src/gpu/glsl/GrGLSLGeometryProcessor.cpp
+++ b/src/gpu/glsl/GrGLSLGeometryProcessor.cpp
@@ -166,7 +166,9 @@
                     localCoords = tr.fLocalCoords.c_str();
                 }
                 vb->codeAppend("{\n");
-                uniformHandler->writeUniformMappings(tr.fFP->sampleMatrix().fOwner, vb);
+                if (tr.fFP->sampleMatrix().fOwner) {
+                    uniformHandler->writeUniformMappings(tr.fFP->sampleMatrix().fOwner, vb);
+                }
                 if (tr.fType == kFloat2_GrSLType) {
                     vb->codeAppendf("%s = (%s * %s * %s).xy", tr.fName,
                                     tr.fFP->sampleMatrix().fExpression.c_str(), tr.fMatrix.c_str(),