Allow spaces before the ascii STL header keyword

The text "solid" is the general STL header indicator that the file is in fact
an ascii STL archive.  Allows spaces to precede the "solid" keyword, providing
compatibility with exporters that insert such (non-compliant )spaces.

code/STLLoader.cpp

@@ -86,7 +86,12 @@ bool IsAsciiSTL(const char* buffer, unsigned int fileSize) {
 	if (IsBinarySTL(buffer, fileSize))
 		return false;
 
-	if (fileSize < 5)
+	const char* bufferEnd = buffer + fileSize;
+
+	if (!SkipSpaces(&buffer))
+		return false;
+
+	if (buffer + 5 >= bufferEnd)
 		return false;
 
 	return strncmp(buffer, "solid", 5) == 0;
@@ -209,7 +214,11 @@ void STLImporter::LoadASCIIFile()
 {
 	aiMesh* pMesh = pScene->mMeshes[0];
 
-	const char* sz = mBuffer + 5; // skip the "solid"
+	const char* sz = mBuffer;
+	SkipSpaces(&sz);
+	ai_assert(!IsLineEnd(sz));
+
+	sz += 5; // skip the "solid"
 	SkipSpaces(&sz);
 	const char* szMe = sz;
 	while (!::IsSpaceOrNewLine(*sz)) {