WERD_RES: Fix uninitialized member variable

Credit to OSS-Fuzz which reported this issue:

    pageres.cpp:1143:7: runtime error: load of value 249, which is not a valid value for type 'bool'
	    #0 0x6ba560 in WERD_RES::Clear() tesseract/src/ccstruct/pageres.cpp:1143:7
	    #1 0x6b9fd1 in WERD_RES::operator=(WERD_RES const&) tesseract/src/ccstruct/pageres.cpp:193:3
	    #2 0x49a9ad in WERD_RES::WERD_RES(WERD_RES const&) tesseract/src/ccstruct/pageres.h:356:11

See https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=13707.

Signed-off-by: Stefan Weil <[email protected]>

Author: stweil

src/ccstruct/pageres.h

@@ -352,6 +352,8 @@ class WERD_RES : public ELIST_LINK {
   // Deep copies everything except the ratings MATRIX.
   // To get that use deep_copy below.
   WERD_RES(const WERD_RES& source) : ELIST_LINK(source) {
+    // combination is used in function Clear which is called from operator=.
+    combination = false;
     InitPointers();
     *this = source;            // see operator=
   }