Changed handling of potential integer overflows on reads

Changed handling of potential integer overflows on reads for bits_kind==int64,
changing max_digits from 20 to 19. Removed comment that my treatment may not be
quite right. Also fixed a typo in an error message.

[ticket: X]

Author: wclodius2

src/stdlib_bitsets.fypp

@@ -27,7 +27,7 @@ module stdlib_bitsets
     public :: max_digits, overflow_bits
     integer, parameter ::                   &
         max_digits = 10 ! bits_kind == int32
-!        max_digits = 20 ! bits_kind == int64
+!        max_digits = 19 ! bits_kind == int64
 
     integer(bits_kind), parameter ::     &
         overflow_bits = 2_bits_kind**30/5 ! bits_kind == int32
@@ -2128,7 +2128,7 @@ contains
             case( read_failure )
                 error stop "A failure occurred in a READ statement."
             case( write_failure )
-                error stop "A failure occurRed on a WRITE statement."
+                error stop "A failure occurred on a WRITE statement."
             end select
         end if
     end subroutine error_handler

src/stdlib_bitsets_64.fypp

@@ -646,7 +646,6 @@ contains
                 digits = digits + 1
                 if (  digits == max_digits .AND. bits > overflow_bits ) &
                     go to 996
-!! May not be quite right
                 if ( digits > max_digits ) go to 996
                 bits = bits*10 + iachar( string(pos:pos) ) - ia0
                 if ( bits < 0 ) go to 996
@@ -779,7 +778,6 @@ contains
                 digits = digits + 1
                 if (  digits == max_digits .AND. bits > overflow_bits ) &
                     go to 996
-!! May not be quite right
                 if ( digits > max_digits ) go to 996
                 bits = 10*bits + iachar(char) - iachar('0')
                 if ( bits < 0 ) go to 996

src/stdlib_bitsets_large.fypp

@@ -835,7 +835,6 @@ contains
             case(ia0:ia9)
                 digits = digits + 1
                 if ( digits == max_digits .AND. bits > overflow_bits ) go to 996
-!! May not be quite right
                 if ( digits > max_digits ) go to 996
                 bits = bits*10 + iachar( string(pos:pos) ) - ia0
                 if ( bits < 0 ) go to 996