PP: Fix issue #407; handle empty identifier.

The sequence

  #define m()
  int m"

creates a token of no length (a string of 0 size).  Protect
against a string of 0 size as well as the existing protect
against a null string.

Test/baseResults/cppBad.vert.out

@@ -1,8 +1,10 @@
 cppBad.vert
 ERROR: 0:2: 'preprocessor evaluation' : bad expression 
 ERROR: 0:2: '#if' : unexpected tokens following directive 
-ERROR: 0:3: '' : missing #endif 
-ERROR: 3 compilation errors.  No code generated.
+ERROR: 0:5: 'string' : End of line in string 
+ERROR: 0:5: 'macro expansion' : expected '(' following n
+ERROR: 0:5: '' :  syntax error
+ERROR: 5 compilation errors.  No code generated.
 
 
 Shader version: 100

Test/cppBad.vert

@@ -1,2 +1,5 @@
 #define m#0#
 #if m
+
+#define n()
+int n"

glslang/Include/revision.h

@@ -2,5 +2,5 @@
 // For the version, it uses the latest git tag followed by the number of commits.
 // For the date, it uses the current date (when then script is run).
 
-#define GLSLANG_REVISION "SPIRV99.1373"
+#define GLSLANG_REVISION "SPIRV99.1374"
 #define GLSLANG_DATE "30-Jul-2016"

glslang/MachineIndependent/Scan.cpp

@@ -612,13 +612,15 @@ void TScanContext::deleteKeywordMap()
     ReservedSet = nullptr;
 }
 
+// Called by yylex to get the next token.
+// Returning 0 implies end of input.
 int TScanContext::tokenize(TPpContext* pp, TParserToken& token)
 {
     do {
         parserToken = &token;
         TPpToken ppToken;
         tokenText = pp->tokenize(&ppToken);
-        if (tokenText == nullptr)
+        if (tokenText == nullptr || tokenText[0] == 0)
             return 0;
 
         loc = ppToken.loc;