Fix fuzzer-discovered error with variable declarations.

As soon as a single VarDeclaration is successfully created, its Variable
is added to the current symbol table. However, if a variable-declaration
line declared several variables in a row, we would stop if ANY of the
declarations contained an error and discard the entire statement, but
would continue processing the rest of the program. This left us in a
position where some Variables existed in the SymbolTable with valid,
reachable names, but their corresponding VarDeclaration statement had
been thrown away as erroneous. Since Variables point back to
VarDeclarations for their initialValues, this gave us a stale pointer.
Any future reference to that variable name which could trigger an
access to its initialValue would read from this dead pointer.

This CL fixes the conversion of VarDeclarations so that we no longer
throw away any VarDeclarations associated with a successfully-parsed
Variable.

Change-Id: If8ec3c160933e48a0e1f36414234b3a849d8978c
Bug: oss-fuzz:32587
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/389636
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>

gn/sksl_tests.gni

@@ -142,6 +142,7 @@ sksl_error_tests = [
   "/sksl/errors/Ossfuzz29849.sksl",
   "/sksl/errors/Ossfuzz31410.sksl",
   "/sksl/errors/Ossfuzz31469.sksl",
+  "/sksl/errors/Ossfuzz32587.sksl",
   "/sksl/errors/OverflowFloatLiteral.sksl",
   "/sksl/errors/OverflowIntLiteral.sksl",
   "/sksl/errors/OverflowParamArraySize.sksl",

resources/sksl/errors/Ossfuzz32587.sksl

@@ -0,0 +1,2 @@
+const float x=1, _=x1;
+half x=x*8;

src/sksl/SkSLIRGenerator.cpp

@@ -457,13 +457,13 @@ StatementArray IRGenerator::convertVarDeclarations(const ASTNode& decls,
                 arraySize = this->convertExpression(*iter++);
             } else {
                 this->errorReporter().error(decls.fOffset, "array must have a size");
-                return {};
+                continue;
             }
         }
         if (iter != varDecl.end()) {
             value = this->convertExpression(*iter);
             if (!value) {
-                return {};
+                continue;
             }
         }
         std::unique_ptr<Statement> varDeclStmt = this->convertVarDeclaration(varDecl.fOffset,

tests/sksl/errors/Ossfuzz32587.glsl

@@ -0,0 +1,5 @@
+### Compilation failed:
+
+error: 1: unknown identifier 'x1'
+error: 2: symbol 'x' was already defined
+2 errors