Fix EXE/DLL cert verification

RSA certificate verification is failing because we accidentally lowered
the max size of numbers for floating point multiplication with
TomsFastMath when upgrading the vendored library code.

This commit restores the default from 4096 to 8192.

Author: val-ms

libclamav/tomsfastmath/headers/tfm.h

@@ -102,7 +102,10 @@
  * You can externally define this or it defaults to 4096-bits [allowing multiplications upto 2048x2048 bits ]
  */
 #ifndef FP_MAX_SIZE
-   #define FP_MAX_SIZE           (4096+(8*DIGIT_BIT))
+// Increase max size of TomsFastMath's numbers from 4096-bits to 8192-bits.
+// 8192-bits was the previous maximum size, but was reduced to 4096 bits (the default) accidentally when the library was updated.
+// The higher size is required for RSA certificate verification.
+   #define FP_MAX_SIZE           (8192+(8*DIGIT_BIT))
 #endif
 
 /* will this lib work? */