fix for SkSL producing invalid branch after an OpKill

src/sksl/SkSLSPIRVCodeGenerator.cpp

Index: src/sksl/SkSLSPIRVCodeGenerator.cpp
diff --git a/src/sksl/SkSLSPIRVCodeGenerator.cpp b/src/sksl/SkSLSPIRVCodeGenerator.cpp
index 037abc03e1c76eae70861ad44cccb72bd1564829..0a2dab3adf7ac14d9be9f9f2ee5d9a3b9181d802 100644
--- a/src/sksl/SkSLSPIRVCodeGenerator.cpp
+++ b/src/sksl/SkSLSPIRVCodeGenerator.cpp
@@ -775,6 +775,7 @@ void SPIRVCodeGenerator::writeOpCode(SpvOp_ opCode, int length, std::ostream& ou
     switch (opCode) {
         case SpvOpReturn:      // fall through
         case SpvOpReturnValue: // fall through
+        case SpvOpKill:        // fall through
         case SpvOpBranch:      // fall through
         case SpvOpBranchConditional:
             ASSERT(fCurrentBlock);